CA1069737A - Screw driver - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

The screw driver is adapted for mating and driving engagement with a recess in the end of the screw which comprises a shank portion and a recessed engaging portion formed at one end of the shank portion. The recessed engaging portion comprising a central core and a plurality of blades radiating from the core. The surfaces of the lower end of the blades are provided with projections. In certain embodiments, it is the intermediate walls between pairs of adjacent blades, which have a concave configuration providing sharp edge at the lower end of each of the intermediate walls.

Description

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. BACKGROU~D 0~ lE INVENTION

1 This invention relates to improvements in fasteners generally and in particular to screws or the li.ke having recesses which are suited to be driven with powered drivers. Among the primary dirficulties which have been presented in connection with the driving Or screws has been to control the torque to wh~ch such screws are tightened by the driver. The difficulties are amplified when power drivers are used. Prior to the develop-ment Or power drivers'with clutch devices, which may be preset to control the torque applied to the screw, the most wideiy used technique for controlling the torque was to design the shape of the driver-receptive recess and the driver so that - they would disengage when a predetermined torque was reached.
For example, U. S. Patent No. 2,046,837 to Phillips shows such a recess in which the walls of the recess are inclined so as to . impart an axial removal force to the driver as the applied tor-que increases, a charactertistic referred to as "cam-out".
While this was generally effective, it required some measure of ~ . .
skill by'the operator in that in order for,the driver to cam-out Or the rec,ess at the desired torque, the operator would have -20 to control the amount of axial force of the driver and would also have to maintain the driving tool in substantially axial, alignment with the screw. Because of the operator-controlled , . variables, it was not uncommon for power driven screws to be over-torqued or under-torqued. In addition, disengagement of the driver would cause the driver to slip ou~ Or the recess and sometimes mar the sur,face of the work. ' . With the development Or improved clutches for po~er drlvers to set a~d control the maximum applied torque, it be . came desirable to provide improved recesses which could be en-gaged by a driver more firmly to retard further the tendency to a ~ :

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.' .. ' . ' 1 cam-out. To this end, efforts were made to design the driver-.- engaged driven surfaces of the recess so that they ~lould be as : . .
.~vertical (parallel to the screw axis) as pGssible to avoid the . camming effect of upwardly and outwardly inclined drive walls.

For example, U. S. Patent Nos. 3,237,506 and Re. 24,878 illus-trate recesses having substantially vertical drive walls.
~',. .
. While a recess having vertical drive walls is generally :: effective to retard cam-out along the axis of the screw when ~, ` the driver is in axial alignment with the axis of the screw, , 10 there still is a tendency for the driver to slip out of engage-.~;. , .
:.~`. ment from the recess when the driver is out of axial alignment ., .

.. with the screw. 'rhis results from the fact that when the driver ~, axi.s -ls out of alignment with the screw axis, the surfaces of , ~- the driver become inc~.ined with respect to the recess surfaces - which, when the screw is driven tends to urge the driver out ~- Or the recess... Thus, a certain degree of skill still is required even when,using a power driver having a slip .clutch in that the driver must be maintained in axial alignment with the screw in . order to fully achieve the benefits of the vertical walled re-`. 20 cess. However, even skilled operators, by reason Or fatigue ,.. - or for other reasons, sometimes may have difficulty in main-~,~ taining the driver and screw in axial alinment. It is among ' ,!' ' -.. . the objects of the invention to provide an improved recess con-figuration which retards the tendency Or the driver to pop-out : Or or otherwise become disengaged from the screw.recess even when there is some misalignment between the driver and the screw.
Also among the prior considerations relating to recessed screws is the.characteristic which is commonly referred to as "stick-fit", a condition in which the recess and driver fit 3 together so that the scre~ will clin~ to the driver when they ~'"' &
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1 are mated. This is de;ir-lible in those instances where it is an advantage to the operator to attach the screw to the driver so that he may then position the screw by the driver and then sim-ply drive the screw into the workpiece. Such a stick-fit often is difricult to achieve with consistency because of variations in manufacturing tolerances. Also, drivers and recess-forming punches wear with use which may result in somewhat less than an ideal stick-fit between a particular screw and driver. More-over, there are instances in which, while a stick-fit is an ~-~ 10 initially desirable characteristic, it may become undesirable if - the fit is so tight that it tends to maintain the stick-fit after the scrçw has been driven. In this regard, many drivers , hold the driver bit in a socket by a magnet which, if the stick fit is retained after the screw has been driven, results in the bit inconveniently remaining stuck to the screw after it has been driven as the magnets employed usually retain the bit only under a light force. It is among the objects of the invention to.provide a screw recess having stick-fit characteris-tics and in which the force employed in drlving the screw de-forms those regions Or the recess which provided the stick-fit, thus destroying the stick-rit and assuring easy removal Or the driver bit.

' . ~ ' . ' ' . ', SUMMARY OF THE INVENTION
In brief, the invention resides in the provisions Or one or more longitudinal ribs formed on the drive and/or back ; out waIls Or the screw recess. Each of the ribs extends along a direction which lies generally within a plane parallel the axis of the screw. Each rib projects slightly from the surface . - ., .
~ 30 of the recess wall into the recess so that when the driver is .

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inserted inl:o the recess it will be engaged by the ribs under a light but sufficient force to enable to screw to cling to the driver. The ribs are dimensioned and located so that even i when the driver is out of axial alignment with the screw (as is ; not infrequently the case) some of the edges of the blade or blades of the driver will dig into the ribs and interlock therewith to retard disengagement of the driver as long as the rotary driving force is applied. The ribs are integral with and are made from the same metal as the screw which typically , 10 is softer than that of the driver a~d will deform under the incluence of the driving force. After the screw has been ~- driven, and because the ribs have been deformed during the dri-ving, the stick-fit is minimized or destroyed and the driver can be removed easily and without difficulty.
The screw driver is adapted for mating and driving engagement with a recess in the end of the screw which comprises .
a shank portion and a recessed engaging portion formed at one .
; end of the shank portion. The recessed engaging portion comprising a central core and a plurality of blades radiating j 2~ from the core. The surfaces of the lower end of the blades are provided with projéctions. In certain embodiments, it is the intermediate walls between pairs of adjacent blades, which have a concave configuration providing sharp edge at the lower end of each of the intermediate walls.
In alternate embodiments of the invention, the driver ~ay be modified to proviide transversely extending ribs on selected regions thereof which will interlock with the ribs .:. . . .
on the recess to enhance the grip therebetween.

It is among the objects of the invention to provide an improved screw recess which retards premature disengagement of the driver from the recess.

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Another object of the invention is to provide an im-. proved screw recess in whlch the driver engaging surfaces thereof ; are provided ~ith one or more longitudinal ribs which extend outwardly of the recess surface.
Another object of the invention is to provide an improved recess of the type described in which the ribs are deform-able and can interlock with sélected regions of the driver.
~ A further object of the invention is to provide a .', . ' - , . :
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~ ~ 7 3 7 : 1 recess whi.ch will receive the driver in a stick-fit yet which ~Jill not tend to cling to the driver after the screw has been ; driven.
- Still another object of the invention is to provide an improved driver having ribs formed at selected locations thereof .. . . . .
- for interlocking engagement with a scre~l recess.
Another object of the invent~on is to provide a screw having a recess in which precise conformity of the driver with the recess is not required for optimum performance.
. 1~ , . DESC~IPTION OF THE D~Al.~INGS
. The foregoing and other objects and advantages Or the invention will be understood more fully from the following .. further description thereof with reference to the accompanying drawïngs wherein: .
FIG. 1 is an elevation of a recessed head screw and . . .
..
. driver in a-mated configuration; .
: FIG. 2 is a plan illustration of a recessed head . . - , .
screw modified to include ribs pursuant to the invention with `-....... the ribs shown in enlarged exaggeration for clarity;
. .
. FIG. 2A is an enlar~edp~an illustratration of a portion the recess shown in FIG. 2 and illustrating, in enlarged -. exaggeration, the rib in accordance with the invention;
FIG. 3 is a sectional Rlevation of the recess as seen . .
... along the line 3-3 of FIG. 2; .
FIG. 4 is a plan vie.w of the recess of FIG. 2 mated with a:driver aS suggested in FIG. 1 with the driver being shown ln section at~the top of the screw as suggested by line 4-4 in FIG. l;
FIG. 5 is a fra~mented illustration Or the recess of ,. ~

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.3/di '7/75 ~ 10~9'~37 ., IC. 2 in enga~ement wlth a driver but with the driver axis being misaligned with respect to the screw axis;
- FIG. 6 is a plan view Or the recess and driver in the configuration o~ FIG. 5 with the driver being shown in section at the top surface Or the screw as suggested by the line 6-6 in FI G . 5;
.~ FIG. 7 is a somewhat diagrammatic illustration Or the ~ relationship between one of the driver blades and its.recess : ,: .
-groove as seen along the line 7-7 Or FIG. 6;

~, 10 FIG. 8 is an illustration of another of the driver ; .~. . .
- blades similar to FIG. 7 and as seen along the line 8-8 Or FIG.
,: 6;

FIG. 9 is a plan view of the recess shown in FIG. 2 : ;. .
further modified to include the ribs, in enlarged exaggeration, Or thç invention on the drive walls and back out walls of the recess grooves.

FIG. 10 is an illustration similar to FIG. 7 and illus-: trating the relationship between a misaligned driver blade and the recess groove configuration shown in FIG. 9;

:.. 20 FIG. 11 is a side elevation of a modified form of .. - driver whicl? may be employed in connection with the inventio.~;

- FIG. 12 is an end view of the-driver of FIG. 11;

FIGS. 13-15 are somewhat diagrammatic illustrations :; taken. in section through a combined recess groove and the blade .. Or a driver shown in FIG. 11 and illustrating the cooperation between the recess groove and the modified driver blade;

FIG. 16 is a side elevation Or a further modified driver;

FIG. 16A is an.illustration Or still another modified form Or driver blade;

FIG. 17 is a sectional illustration Or a driver blade ' ~

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1 as seen along tlle ].ine 17-17 Or FIG. 16A;
.~ FlG. 17A is an illustration similar to FIG, 17 and .
; showing a variation Or the configuration shown in FIG. 17;
FIG. 18 is an illustration similar to FIG. 17 showing a .. furtller variation thereor;
FIG. 19 is a side elevation of a driver blade embodying a further variant of the invention;
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FIG. 20 is a sectional illustration of the variant Or FIG. 19 as seen along the line 20-20 of FIG. 19, ,j~!, 10' FIG. 21 is a side elevation of still another modifica-- tlon of the invention;
- FIG5. 22-24 are illustrations of further configura-~ tions for the drive and/or back out walls of the recess grooves;
- FIG. 25 is a somewhat diagrammatic sectional eleva-tion, similar to that of FIGS, 7 or 8, illustrating the phenomen-. on Or fall away in-a c.old formed recess groove;
FIG. 26 is a fragmented illustration Or a combined . re$ess sbrew.and driver .in which the screw has a significant amount Or fall away;
FIG. 27 is an illustration Or one blade of a drlver which may be employed advantageously with screws having signi-.. ficant amounts of fall away;
FIG. 28 is an illustration Or a modified form Or drive.r having recess-ei;gaging ribs-at locations between the ~; .driver blades, FIG. 29 is a fragmented sectional illustration of a portion of the driver Or FIG.28 as seen along the line 29-29 Or FIG. 29;
. FIG. 30 is an illustration sim~lar to FIC. 29 showing an alternative to the structure sho~n in FIG. 29;

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` ' 1 FIG. 31 is an illustrat on oP a recess having a rib inc~uded th~rein in accordance wlth a further aspect of the invention in which the rib is disposed at that portion which defines the central portion of the r~cess;
`~ ~ FIG. 32 is a plan view Or the configuration shown in FIG. 31;
FIG. 33 is an illustration Or a further variant Or . .
: the driver shown in FIG. 28;

FIG, 34 is a plan view Or a recess having inclined ;, ...
.~: 10 side-walls and being provided with ribs in accordance with .another aspect Or the invention in which the ribs taper down-.:.-.-~ wardly with respect to the groove walls from which they protrude, ,:;
. the ribs being shown in enlarged exaggeration;
FIG. 35 is an enlarged plan illustration of one of therecess ~srooves Or FIG. 34;
FIG. 36 is an illustration Or the recess shown in FIG. 35 as seen along the line 36-36 of FIG- 35i FIG. 37 is an illustration of the recess groove shown in FIG. 35 as seen along the line 37-37 Or FIG. 35;
FIG. 38 is an illustration similar to FIG. 36 and .... .
-.~ showing a further variation in the configuration Or the rib;

FIG. 39 is a plan view Or the invention as incorporated ::. in another type Or recess with the ribs shown in enlarged , ~ . , .
~i exag~eration;

. ~ . FIG, 40 is a sectional elevation of the recess shown , ~ . . .
in FIG. 39 as seen along the line 40-40 Or FIG. 39 j : FIG. 41 is a sectional elevation of the recess of FIG.
. . . .
39 as seen along the line 41-41 of FIG. 39;

' FIG. 42 is an illustration similar to FIG. 41 showing ., 30 a modified rib which is inclined downwardly and inwardly;
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." ~.AZB/~ 973,7 ~.'' . , ' ' 1 FIG~ ll3 is an il.lustration of the rib configur,ation Or FIG~ 42 as'seen in ?lan;
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FIG~ ~4 is an illustration of the invention as ineor-porated in still another type of recess; '' ~' ; FIG~ 45 is an illustration of the recess shown in ;. - ~ .
FIG~ 44 as seen along the line 45~45 of FIG~ L14;
FIG~ 46 is an illustration of the recess shown in FIG~ 44 as seen along the line 46-46 of FIG~ 44;
FIG~ 47 is an illustration similar to' FIG~ 45 showing .. lO a further vari.ant of the rib configuration;
FIG~ 48 is an elevation Or a back out wall of'the recess of FIG~ 44 as.seen along a direction suggested by the line 48-48 of FIG~ 114 and modified to include ribs in accordance with the ; . invention;
FIG~ 49 is an'elevation of a conventional driver used ~'~. in connection with the -recess sho~n in FIG~ 44;
. . .
FIG~ 50 is an end view of the driver. Or FIG~ 49;

.''- FIG. Sl is a side elevat'ion of the driver of FIG~ 119 ;.~ , .
. ', modified to include a configuration of ribs in accordance with ' - ' one aspect,of the invention;

FIGo 52 is a s~ide elevation of a portion of the driver ', . . of FIG. 49 showing a further variation in the rib configuration '' o~ a driver blade;
, .. . . . . .
i ~ FIG~ 53 is a side elevation of a further embodiment of ~:;
~,~ the friber;

i FIG~ 54 is a side elevation of a portion of the driver ,~', ' showing the back out wail and the manner in which it may be .. ' hollowed out to engage the.recess;

FIG~ 55 is an illustration as seen along the line 3~ 55~55 Of FIG. 54;
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',''' 1 FIG. 56 's a side elevation Or a protruding head for.: . . .:
a screw rastener ~odified to include the invention;, and ;'~ FIG. 57 is a plan view of the fasteners shown'i'n FIG.
, 56 and illustrating, in section, the manner'in which the head ~,~' is engaged by an appropriate driving tool.
FIG. 58 is an end view of a punch which may be employed 'i to fabricate the recess shown in FIGS. 2 and 3;
'~ FIG. 59 is a side elevation of the punch shown in FIG.
.. . .
~' 58;
~; 10 FIG. 60 is an end view of a punch which may be employed .
to ~abricate the recess shown in FIGS. 34-36;
,, FIG. 61 is a side elevation of the punch shown in ~'~
; FIC. 60;
FIG, 62 is an end view of a punch which may be employed ... . .
;' to fabricate the recess shown in the FIGS. 31 and 32; and ,,~ , - , FIG. 63 is a side'elevation of the punch shown in FIG.
,- 62.
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. .
'- DESCRIPTION OF THE PREFERRED EMBODIMENTS
... .
', FIG. 1 shows a combined recessed screw 10 and driver 12 ' 20 with the driver seated ideally,in the recess and in axial align-,-; ment with the screw. While the particular recess and driver ,~ shown is that described in U. S. Patent No. 2,474,994 to Tomaiis , .............. . .
i;' the prin,ciples Or the invention may be employed with other types rec~sses and screw head configurations, as will be apparent.
FIGS. 2 and 3 illustrate the Tomalis recess modified to include ;' one form Or the present invention. The recess in this embodiment shown is Or polygonal form and may be defined as generally cruci-;' form in plan. The recess includes a central portion 14 and a . .

~ - plurality Or grooves 16 radiating outwardly from th'e center por-,,', 30 tion 14. ,The' grooves 16 are separated from each other by ' ' . .
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'~. 10 , .............................. .
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~ 0~'73 7 1 downwardly and in~ardly inclined recess intermediate walls 18.
The bottom regio;l: Or the grooves lG and walls 18 merge into a generally concave recess bottom 20. Each of the grooves 16 is defined by a pair of triangular sidewalls 22, 22' and an end . wall 24 which is inclined downwardly and inwardly. In the Tomalis scr.ew illustrated, the groove sidewalls 22, 22' also ~ are inclined but at a compound angle in which the planes of the .` sidewalls 22, 22~ converge both in a downward and in an inward .~ dire~tion as defined more fully in the Tomalis patent. In the following description of the invention the screw and recess ;~ will be considered as right handed, in which sidewall 22 would ~ be considered to be the driving wall when the screw is being .~. fastened and in which the opposite side~all 22' ~the back out .. . .
wall) will function as the driving wall when the screw is being remoyed.
: . . . In accordance with the invention, tile driving walls ` 22 of the recess grooves 16 are provided with longitudinal ribs 26. In the embodiment shown in FI~S. 2-7 the ribs 26 extend - from the intersection of the drive wall 22.and end wall 24 of ~ 20 the groove upwardly toward.the intersection of the top 27 of i; the scréw head with the.drive wall 22. The configuration and number of ribs 26 is subject to a number of variations, as will . . . .
. be described. In this configuration shown the rib 26 is of ;- genera~ly triangular cross-sectional shape having an apex or . - ridge 28 and sidewalls 30 which merge with the drive wall 22 .
~see enlarged FIG. 2a). The rib 26 extends the full height of the drive wall 22 and is located at the radially inward region of the drive wall 22, in proximity to the juncture of the drive wall 22 and.the intermediate wall 18. The rib 26 protrudes rrom the drive wall 22 just slightly, for example, Or the order .

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`'.' . , -1 of a few thousandths of an inch or less, depending on the ''j size Or the fastener, the illustration Or the ribs herein .. . .
being highly exaggerated for purposes Or illustratlon. The ~;~'' apex 28 o~ the rib 26 faces inwardly toward the groove 16 ;'-' and substantially parallels the plane of drive wall 22. The rib also extends along a direction which generally lies within a plane parallel the screw axis. In the embodiment shown in ' FIGS. 2 and 2A the sidewalls 30 lie generally in planes which ^ do not parallel the screw axis and when viewed from the axis . ~ , ~; 10 of the screw, as in FIGS. 2 and 2A, the surfaces of the rib sidewalls 30 will be exposed. As will be described with regard - to other embodiments of'the invention, the sidewalls of the , .............. . . .
~ rib 26 may be formed to lie in planes which do substantially ,~, . .
~' parallel the axis of the screw, in which case the ridge 28 will ~, . . .
also parallel the screw axis. In the embodiment shown in FIGS. 2 and 2A, however, where'the sidewalls 30 are inclined as ' described, the ridge 28 will also be disposed generally askew ~-~ to the longitudinal axis Or the screw so that the rib 26 may receive the blade Or the driver in a wedged fit.

As shown in FIGS. 1, 4 and 6 the driver may be of "~ ~Jr conventional design having a shank 32 and a bit formed at the " end of'the shank, the bit being generally complementary to the ., - . . .
r, ,~ recess. The bit is formed to define blades 34 which extend from . :" . . .
~'"' a central core ~3 and are equal in number and spacing to the .... .
~' grooves 16 in the screw recess. Between each pair of adjacent ~' ' blades 34 the core 33 of the driver bit is defined by intermed-~:' . , .
~' iate walls 36 generally complementary to the intermediate walls 18 Or the recess. The bottom 38 Or the driver may be formed ' With a generally conical tip similar in shape to the bottom 20 ' 30 Or the recess.
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'- 106~73'7 , 1 It may be noted that in the recess and driver described in the Tomalis patent a "stick-fit" characteristic is achieved by dimensioning the intermediate walls 36 Or the driver and intermedia~e walls 18 of the recess so tha~ when fully mated they engage in a close, wedging fit while the thickness Or the driver blades 34 is slightly less than the width of the recess grooves. While under ideal manufacturing conditions the Tomalis recess and driver may be formed to achieve the desired wedging effect, the more usual manufacturing conditions often result in a recess-driver fit which is less than ideal. For example, as the punch employed in cold forming the recess wears - from use, the resulting recess may not receive the driver in the intended manner and may not perform as intended. Also contributing to t~le difficulties encountered with the Tomalis recess is the phenomenon sometimes referred to as metal "fall-away" in which the upper regions of the groove sidewalls,-as they approach the top surface of the screw head tend to curve ; outwardly and away ~rom their intended location. This results in a progressively enlarged recess configuration near the upper `cO portions of the recess which contributes to premature disengage-ment of the driver with the recess, particularly when the driver is slightly out os axial alignment with the screw.

.. . . .
: By providing the recess with the ribs 26 in accordance : with the invention, the above difficulties may be reduced - materially. The ribs 26 are dimensioned to project into their ;~ respective grooves 16 so that they will present a slight inter-ference with the blades 34 of the driver which are inserted into t:'~'' the recess grooves, Because the ribs 26 are of relatively small cross-sectional dimensions they enable the screw head to be manually applied onto the end of the driver in the desired ~"''' .
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1 stick-rit. The ribs 26 wlll perrorm their intended function even where a particular screw exhibits a substantial degree Or metal fall-away. Such fall-away usually is confined to the upper portions Or the screw recess, Where thc ribs 26 extend .
downwardly to the bottom Or the drive wall 22, at least the lower portions of the ribs 26 will be properly located to en-,;, gage the driver blades 34 and cling to them. When the screw is driven, the force Or the driver blades 34 against the .
~: slightly pro~ecting ribs 26, particularly at the end Or the driving procedure where the resistance to torque is substan-tially increased, deforms the ribs 26 which are quite small - and deformable in relation to the strength Or the driver. The ~~~ ribs 26 derorm to an extent surficient to destroy the stick-; fit characteristic thus enabling the driver to be withdrawn easily and without any tendency to remain stuck to the screw.
.
:~ The manner in which the ribs 26 retard the tendency for the driver to disengage from the recess during dr-iving when the driver and screw are slightly misaligned may be seen , from ~IGS. 5-8. FIG. 5 is a fragmented illustration of a .,;
combined recess and driver in which the driver axis 40 is slightly f-\ misaligned rrom the screw axis 42 as suggested by the angle A.
; .
The driver also is slightly withdrawn from the recess as is ..:-.,. , typically the case when the driver and screw are misaligned.
,....
~ FIGS 5 and 6 illustrate the relationship Or the driver and -;~ recess when the misalignment is directly to the right Or the .-- recess axis as seen in those figures and as suggested by arrow ,::
-:: 44 in FIGS. 5 and 6. When this condition occurs with the ';' ::~ screw being driven in a clockwise direction, the primary contact between the driver and recess occurs beti~een driver blades 34a and 34c with their respective grooves. Driver blades 34b and '. ., ~ - ' '.

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., 34d, which lie generally along the directlon of misalignment of the driver, efrect little, ir any~ significant grip on any of the surraces of their respective recesses. Thus, as shown in rurther exaggeration in FIGS.'7 and 8, the primary regions of contact between each Or the driver blades 34a, 34c and their grooves will be at the region or-engagement between the lower portion Or one side of each of the driver blades 34a,'34c with one sidewall of the recess groove and the other region of contact will be between the upper portion Or the opposite surraces Or the blades 34a, 34c with a more upwardly disposed portion Or the opposite sidewall of their grooves. As seen in FIG. 7 the lower portion Or the driving surface 46 Or blade 34a will bear toward the driving wall 22 o~ its groove 16 which will cause the lower edge 48 of the blade 34a to dig into the rib 26 on the wall 22. ~his engagement of the driver blade with the rib results in an interlocking between the two which tends to retard ~urther withdrawal Or the driver from the recess.

.
As the rotation of the screw is continued but ~rith the -- attitude Or axial misalignment remaining the same it will be '20 seen that as the blades 34 approach a further rotation Or 90 , blade 34a wiil progresslvely decrease its engagement with its associated rib 26 while blade 34d progressively shirts to a more , misaligned 'attitude in its respective groove, to the angle Or misalighment A between the driver and screw. As blade 34d is . .
progressively rotated to the'misaligned attitude within its recess the lower edge 48 Or blade 34d progressively digs into and interlocks ~rith the rib 26 associated with that groove.
~' Thus, as the screw is driven, the blades 34 successively dig lnto an'~ release from the ribs 26 and in a manner which contin-ually retards the tendency of the misaligned driver to be urged . .
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ef_ 10ti973~7 1 out Or the recess. It also ret.~rds the tendency ror the angle of misalignment to be increased.
With regard to the embodiment described thus far it .' may be noted that while blade 34c is canted within its recess groove (FlG~ ~! its inclination with respect to the drive wall '~ 22 is reversed from that of blade 34a, so that the driving surface 46 of blade 34c will engage the upper region of the rib 26 in that ~roove. While this may tend to flatten out the upper region of the rib it will not enable blade 34c to dig into the ' 10 rib. In order to enhance the overall grip between the mis-', ~ aligned driver and the recess, it nlay be desirable to provide a rib 26' on the other, back out wall 22' of' the groove 16 as ' '' shown in FIGS. 9 and 10. Thus, when a blade 34 is in the '. position o'f blade 34c, the lower edge portion 4~' of the blade will engage the rib 26' on the back out wall 22'. Thus, the .' . blades in the positions of blades 34a and 34c each will contri-- bute to retarding Or withdrawal of the misaligned driver.from '~ the recess when in the configuration shown in FIGS. 5 and 6.

. ~ The foregoing cooperation between the driver and recess may be enhanced further by providing a driver in which s'elected . ~~ of the recess engaging surfaces of the blades are formed to '~ increase the interlocking effect between the blades 34 and the - ribs 26, FIGS. 11 and 12 show a modified driver in which the blades 34 include ribs 50 formed on.the lower regions of their driving f`aces 46. The drive'r ribs 50 may extend generally . transversely of the axis of the driver as shown and, in general, .. the driver ribs 50 should'extend along a direction such that when the driver blades 34 are inserted into the recess'grooves '.'. 16 the driver ribs 50 will cros.s and intersect with the ribs 26 on the recess drive walls 22. The driver and its ribs 50 which a ~ .

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1 typically are made from a harde~ meta]. than that from which the scre-~J afid its ribs 26 are made will cause the driver ribs :: 50 to cross and di.~ into the recess rlbs 26 under the influ-ence of the applied torque as suKgested somewhat diagram-matically in FIG. 13. If the driver and screw are axially mlsaligned, the driver ribs 50 may aid in digging into the -- recess rlbs 26 as suggested in FIG. 14 which provides a some-. what better interlock between the blade and the rib 26 than .~. .
that as suggested in FIG. 7. The driver may also include at - 10 least one additional driver rib 50a on the driving face 46 of the blade 34 so that in the eve.nt of a misaligned driver and screw, a blade in the position Or blade 34c in FIG. 6 will ~` be able to engage and dig into the upper region of the recess .... .
. rib 26 as suggested in FIG. 15.

. Where the recess groove is provided with ribs 26, 26' on each of the groove walls 22, 22', as suggested in FIGS. 9 and 10, the driver also may be provided with transv~rse blade ribs 50a, 50a' on.b.oth of its driving and back out surfaces as sug-. gested in FIG. 16. In some instances it may be desirable to provide one or more additional ribs on the driver blades inter-: '~ mediate the ribs 50, 50a and 50', 50a'. It should be noted, ... . however, that the number of ribs on each surface of the driver : . . blades 34 preferable should not be too great in number or too :~ closely spaced as this would tend to reduce the ability of the driver ribs 50 and/or 50a to deform and interlock with the . recess ribs 26.

The principles described above with regard to the provision of ribs on the driver blades may be employed with ;. . other configurations. For example, as shown in FIGS. 16A and .: . . . .
. 30 17 a rib 52 may be provided along the lower edge of the blade 34.
: ' . ' .
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8/~/~5 ~ 3'~
. , .
1 The rib 52 may be in the form of a projection as shown More clearly in FIG. 17 or may be formed effectively by hollowing : , .
the lower region of the face 46 of the driver blade as sug-gested at 54 in FIG. 17A to leave a relatively sharp rib 52 - extending t}lerefrom. FIG. 18 is an illustration similar to FIG, 17 but showing that ribs 52 and 52' may be formed on each - lower edge 48 of each driver blade. Moreover, in some instan-ces it may be desirable to provide further ribs in addition to the edge ribs, as suggested in FIG. 19 in which a second rib 52a is formed parallel to the rirst edge rib 52. The ribs 52, -~ ~ 52a may be formed on each side of the blade as suggested at 52',52a~ in FIG. 20. FIG. 21 illustrates a further variation in which a plurlaity of driver ribs 52, 54 are provided on the ~ace or faces of the blades and which they extend along differ-ent directions which neither parallel each other or the axis of the driver.
Still further modifications may be made with respect to the use of the ribs 26. For example, in some instances it may be found that satisfactory results are obtained when the rib does -~ 20 not extend fully to the top of the sidewall 22, or 22' of the ~ groove but, instead, terminates before it reaches the upper end as suggested in FIG. 22. Additionally, there may be instances in which it is found to be desirable to employ a plurality of ribs 26 on either or both of the sidewalls 22, 22' of the recess grooves as suggested in FIG. 23 which shows a plurality Or such ribs 26 in which the upper ends of the ribs lie generally along a line which parallels the end wall 24 of the particular recess groove 16. FIG. 24 shows a further variation in which the recess - sidewall has a plurality Or ribs 26 and in which each rib 26 extends fully from the bottom to the top of the sidewall.

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1 The ph~nomcllon Or metal I'all-away, réferred to above, results in a'screw havirig an imperfect recess, the degree of - irnperfection depending in part on the extent of matal fall-away.
' FIG. 25 is a sectional elevation of a recess groove as seen in a manner similar to FIGS. 7 or 8 but illustrating the effect .
of metal fall-away and the resulting groove configuratiorl. As can be seen, the upper regions of the walls 22, 22' do not merge with the top surface of the screw in a well defined manner but instead, fall outwardly and away from their intended lgcation (indicated in phantom at 57 in FIG. 25) with the result that a substantial portion of the upper regions Or the walls flare upwardly and outwardly, in generally arcuate configuration.

;. ,~ ~-:
:' ' Reces'ses having a substantial amount of fall-away have an adverse' effect on the functioning of the recess in that they provide a r ; reduced driving wall area. In addition, because of the arcuate flare~ surface at the upper region of the'recess wall, fall-away - results in a more wobbly fit between the recess and the driver :. . . .
which, in turn, increase the tendency for the driver to become '~ ' misaligned and cam-out or otherwise pop out of the recess. As . . .
~'' 20 may be seen from the fragmented illustration in FIG. 26 when ;~. . .
~.; ~ the driver and screw are misaligned and with the driver partly ~, . . 1~
withdrawn from the recess, the outer face 56 of the blades there blade 34d) may bear against the outer top ed~e 58 of its associated recess groove. This results from the fact that the misali~nment is not limited by engagement of the opposite drive and back out faces 46, 46' of the blades 34a, 34c with their respective recesses as was shown'in FIG. 5, because the upper re~ions of the sidewalls 22, 22' have fallen away and cannot engage the upper portions of faces 46, 46' Or the driver blades.
When this situation is presented, the primary contacting regions between tiie misaligned driver and recess will be at the lower a 19 ', 8~8~5 ~ :10~73'7 .
1 region of the drivin~ face 46 of blade 34a wi~h drive wall 22 Or its recess, the lower region of back out face 46' Or bla~e . 34c with the back out wall 22' of its associated recess and the : end wal]. 56 Or blade 34d with the upper region 58 of end wall 24 of lts associated groove. In order to effect a more firm grip betwee.n the misaligned driver and screw, the end wall 56 ~:. of the driver blade may be formed to define serrations 60 (See ~ FIG, 27) which can engage and effect somewhat of a grip on the - j upper portion 58 of the recess end walll24.
. It sometimes occurs that when the driver and screw are . ~ ~ misaligned and ~ith the driver slightly withdrawn from the I recess, the primary points Or contact between the driver and 1 recess are not between the driver blades 34 and recess grooves ~ 16 but are, instead, between the intermediate driver walls 36 ¦ and çorresponding intermediate walls 16 on the screw. While ~ i this condition is more likely to occur when a particular screw -:~ has a significant amount of fall-away, it also may occur with a .i: satisfactori.ly -rormed recess such as that shown in FIGS. 2 and . 3 when the driver is misaligned and when the screw has been -.
~--. ; 20 rotated approximately 45 from its orientation shown in FIG. 6 .. . ~~~. to the position suggested in phantom at 16' in FIG. 6 (i.e., . the screw recess is in a position in which the direction 44 of misalignment generally bisects a pair of adjacent engaged driver . blades and recess grooves). In order to resist further the ten-dency of the misaligned driver and recess to disengage when in thi.s temporary attitude, the driver may be modified at the lower . regions Or its.intermediate wall 36. The lower portion of the .. wall 36 is formed to define a rib 64 or protrusion which extends substantially fully alon~ the lenF,.th of its lower edge 62, from the .lower end Or the driver surface 46 of one of the blades 3l1 to `'. '' 2n , . ~
., `." ' ........ .

8/8/ ~5 ~ ~OG~ 3'7 1 the lower end of the back out surface 46' Or the next adjacent blade 34, Wherl the d.iver and screw are in the configuration described the rib 64 at the lower end of the driver wall 36 will be urged against the lower regions of the recess inter-mediate wail 36 and will tend to effect a grip therebetween, further retarding the tendency of the driver to disengage from the recess when in this configuration. The rib 64 may be formed in a variety of ways, including, for example, the hollowing out of the lower portion of the driver wall 36 as shown in FIG. 30. The hollowed out portion 66 may be made in a manner which will leave a relatively sharp edge 68 at the lower edge 62 of the driver wall 36 which will further tend to dig into the wall 18 of the recess. The recess itself may be ., .
modified as suggested in FIGS. 31 and 32 by forming it to include a rib 70 extending from the bottom of the wall 18, where ~........................ - . - .
: it meets the recess bottom 20, upwardly toward the top of the . . , wall 18. The rib may extend fully to the top of the wall 18 as shown or may terminate below the top Or the wall 18. The rib 70 should lie in a substantially vertical plane (one which parallels or coincides with the longitudinal axis of the screw).
~ In addition to providing a rib 64 or sharp edge 68 at - the lower edge 62 of the driver intermediate wall 36, the more ' upwardly disposed surfaces of driver wall 36 also may be provide-ed with a rib 64a as suggested in ~IG. 33. When the screw is in . .
the 45 rotated position described above, it may thus engage the walls 18 on one side of the recess at their lower region and at the upper region of the walls 18 on the opposite side .
of the recess. Where ribs 64a are provided on the upper regions of the driver intermediate walls 36 it is preferred to employ recess wall ribs 70 which extend fully to the top of the recess .

', ~ .

; .
:1 8/~75 - ` ~OG~3737 1 so that the ribs 64a may engage the upper ends of the recess ribs 70. ~he driver ribs 64a should be located on the driver such that they will be below the top surface 27 of the screw even when slightly withdrawn from the recess.
- Still further modifications may be made to the recess ribs 26 described above. For example, in the fore-going des-cription the ri~s 26 were shown as being of substantially uni-form cross-sectlonal configuration and having a ridge extend-i~g substantially parallel to the plane of the recess sidewall from which t}le ribs prOJeCt. In some instances, however; it may be desirab]e to modify the configuration of the rib as shown in FIGS 34-36 in ~Jhich the rib 72 has an edge 74 which substantially parallels the axis of the screw. In this varia-.
tlon the generally triangular cross-sectional area Or the rib . ~ , .
increases in an upward direction when the groove sidewall from which the rib extends is inclined upwardly and outwardly.
; Alternatively, it may be desirable in some instanc~s to employ - a rib 76-of a configuration in which its ridge 78, as shown in FIG. 3g is neither parallel to the screw axis nor to the side-wall plane but still lies within a substantially vertical plane.
In this embodiment, the height of the rib 76 as measured from thè plane of its associated sidewall would be intermediate that o~ the rib configuration shown in FIGS. 34-36 and-the rib configuration described with regard to the embodiment shown in FIGS. 2 and 3.
While the various aspects of the invention have been descr~bed thus far as being employed primarily in connection witli a recess of the Tomalis type having inclined groove side-walls, they may also be employed with other recesses. For exampie, FIG. 39 shows, in plan, a type o~ screw recess which .' '~' ' . .

.

..... , .
"" ' ' ~ ' 0~73'7 1 is comrnerc~ally available and which is described more fully in U. S, Patent No. ~e. 24~878 to Smith et al. In general, that recess includes a central portion 80 and a plurality of grooves 82 extending outwardly from the central portion 80 with each of ~ .
.-- the grooves being defined by a downwardly and inwardly incli.ned end wall 84 and substantially vertical driving and back out walls ` . 86, 88. This recess may be modified in accordance with the ~nvention by forming it to also include vertical ribs 90 on either or both of one or more of the driving or back out walls . 10 86, 88 as suggested in FIGS. 39-41. As shown the ribs 90 are .of substantially uniform cross-section, generally triangular, having a pair of sidewalls ~2 which meet at an apex 94. ~ach rib 90 extends along a direction which lies substantially along a generally vertical plane. The rib 90 extends from the bottom `. of the sidewall and may terminate at the upper edge of the ~- : sidewall or, if desired, somewhat below the upper edge of the sidewall. In additi.on, it may.be found desirable in some in-~,- - stances to f.orm the ribs 90 so that they taper upwardly as i; .: , -suggested in FIGS. Il2 and 43 from which it may be seen that the .

cross-sectionai area of the rib diminishes in an upward direc-:, .
. tion. The ribs 90 are effective to provide a stick-fit in co-operation with the driver as described above. It may be noted ,. . .
that here, as in the previously described embodiments, the re-.. lative dimensions of the rib, particularly the extent to which . they protrude from their substantially vertical sidewall of the - groove is bxaggerated substantially in the drawings for clarity.

It is intended tha~ the ribs extend just very slightly from the ~. sldewall with which they are associated, for example, of the ;- . .
order of a few thousandths of an inch, just enough to enable the ribs to clinG to the engaged surfaces of the driver. The ribs '',"' ' ' ' . 23 '; &
.

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.,, _ ... . .... . . . . .. ........ ... _ _ ... _ , _ _ I~JV.' ~I .1 -~j8~i5 ` lQ~jg73'7 . i are dimensioned ~o that they mar be derormed.under the increas-ing torque of the driver to destroy the stick-fit characteristic as described.
A commercially available variant of the recess des-. - cribed in U. S. Patent No. Re. 24,~78 is that shown in FIGS.
44-4~ which has three grooves 96 extending outwardly from the c~ntral portion 98 of the recess. While the four-grooved recess shown in FIG~ 39 displays relatively little tendency to dis- :
~, ~ngage the driver, the three-grooved variant Or the recess some-`¦ 10 times presents a tnedency for the driver to rock out or spin .., .
I ~ out Or the recess, particularly with smaller sized screws. This .~¦ recess, too, may be modified to include a longitudinal rib 100 - on at least.one Or the sidewalls as suggested in FIGS. 44-46 ~1 ........ to provide the stick-fit characteristic which, while desirable 1 with this recess, has not been readily achievable. Should it ¦ be desired to modify the three-grooved recess to retard the . tendency Or the driver to disengage from the recessj one or ~ more such ribs 1:00 may be provided in association with at least :~ ~ one of the sidewalls of each of the grooves. Thusl as shown in FIGS. 44-46 the driving wall 102 of each of the grooves 96 may be provided with at least one rib 100 which is disposed prefer--.
, . . . .
ably near the inner re~ions of the driving wall 102. The ribs . 100 extend from the bottom of the sidewall 102 upwardly toward , . i ..
the intersection of the sidewall and the top surface 104 of the screw. If desired, the ribs ioo may terminate below the top surface 104 of the screw in the same manner described previously .. or may e~tend fully to the top surface 104 as shown. Further . variations may be employed in the location and number Or ribs such . as suggested in FIG. 47 in which a plurality cr spaced parallel . 30 rlbs 100, are formed on the sidewall 102. Similarly, as shown in .
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~73'7 .,, FIG. 48 the ribs 100' may be formed on the back out wall 106 if desired. In this regard it may be noted that in the three-grooved variant of this type of recess, the back out wall 106 of each groove 96 is longer than the drive wall 102 of the groove in that the more inwardly disposed portions 108 of the back out wall also serves to define the central portion 98 of the recess, the innermost end 108 of the back out wall 106 merging with the drive wall 102 of the next adjacent groove.
The ribs 100' may be provided on the inner portions, outer portions or both portions of the back out wall 106 as shown in FIG. 48.
. . ,b' ,` The foregoing modifications to the three-grooved `- recess described may be employed in connection with a conven-tional substantially complementary three-blade driver shown in FIGS. 49 and 50. It may be desirable, however, to modify the driver to enhance further the grip between the driver and - recess and FIGS. 51-55 illustrate various modifications of the conventional three-blade driver. As shown, the conventional three-blade driver configuration includes a central portion or core 109 from which three driving blades 110 extend, generally radially, each blade 110 having a driving surface 112 and a black out surface 114 which substantially parallel each other - and lie along substantially vertical planes. Each of the blades 110 includes a lower edge 115 at its driving surface.
The back out wall 114 associated with each blade may be con-sidered as having an outer portion 116 which is received in the recess groove and an inner portion 118 which partly defines the core 109 of the driver and which fits within and against the inner portion 108 of the back out wall 106 of the recess.
The lower edge 117 of the inner portion of the back out ~,................................. .
wall of the driver may be substantially '"';
- - 25 _ .
., .

- .,.~ 5 ' - 10~S~73 7 1 horizontal. The driver may be nlodified in a rnanner similar ~o ~' that described previously by providing one or more transve~se ribs 120 on thc driving face li2 Or each blade to dig into and engage the ribs 100 on the corresponding surfaces of the recess.
Alternatively, one or more ribs 122 may be formed on the driving j surface 112 Or the blade substantially parallel to the lower inclined edge 115 and one such rib 122 may be located at the ¦ lower inclined edge 115 (FIG. 52). A further variation is shown in FIG. 53 in which the rib 124 extends from the lower edge 115 of the drive surface substantially continuously along the lower edge 117 of the back out surrace of the driver. In a further variation the back out wall may be somewhat hollowed out near its lower edge as suggested at 126 in FIGS. 54 and 55 to derine - I
a sharp edge 128 which may engage rirmlv the corresponding sur-face of the recess defining portion Or the back out wall on the ¦ screw recess.- Further variat1ons may be employed, for example, t in which the upper regions Or each Or the driving and baclc out ~¦ surfaces Or the driving blades are provided with substantially - transversely extending ribs for engagement with the correspondin~
surfaces Or the recess in a manner similar to that suggested in FIG, 16. ~hile it is believed that these will be most effective in conjunction with a recess having upwardly extending ribs engageable with the transverse ribs on the driver, the modified driver is believed to increase the effectiveness in retarding the tendency to pop out even in the absence of ribs on the recess.
Certain aspects Or the invention may be incorporated into other types of screw fasteners. For exarnple, FIGS. 56 and 57 show a screw fastener-having a protruding head described more rully in U. S. Patent No. 3,584,667 to Reiland. The head includes an upwardly extending driven member 130 having generally , a ''''1 ! ~ .

~O~j~t 73 7 :j 1 serpentine peripheral surfaces which are arranged to define a series of drive walls 132. One or more of the driving wall surfaces 132 Or the member may be provided with upwardly extend-ing ribs 134 in substantially the same manner as described ' herein. The ribs 134 preferably are located at those regions of the drlving surface where the driving tool 136 will exert maY.imum driving torque so that the ribs 134 may be deformed to - destroy the'stick-fit property as the screw is tightened.
', It should be noted that the embodiments of the invention described with regard to recessed screw head configurations have ' been described in connection with flat head screws. The various . aspects Or the invention may be employed with equal effectiveness ~' , , with other screw head configurations. The various recess con-figurations may be formed by conventional cold heading machinery.
' The various recess rib and driver rib configurations may be em-- ployed independently of each other or in various combinations.
The recesses may be ernployed with conventional drivers or modified dri~ers descr,ibed herein, as desired.
,"` ~he various recess configurations described above may be ;.r,'~ 20 formed by conventional techniques in commercially employed heading :
machines, FIGS. 58 and 59 illustrate a punch of a configuration ' which is adap'ted to form the recess shown in FIGS. 2 and 3. The ... . .
punch, indicated generally by the reference character 150, may,be ' ; ' .
~'~ formed in accordance with conventional punch forming techniques.

''~ The punch 150 includes a body portion 152 having a face 154 and , an integral nib 156 which protrudes from the face 154. The nib 156 is the complement Or the shape of the recess and the face 1~4 ~ Or the punch 150 is of complementary shape to that of the intended `'',~ screw head, here described for purposes Or illustration as a flat head, The nib 156 includes a central core 158 and a plurality Or , ' 27 &

, __,.. , . . . .. .. - .

~ f ~
0~9~3 7 . 1 blades-160 t;rhich extend ~enerally radially and outwardly from the core. Each of the b].ades 16Q has a pair of side surfaces 162, 161J and an end surface 166 which is inclined upwardly and outwardly from the outer region of the core 158. The blades 160 at their upper ends, merge i.nto the ~ace 154 of the punch-to define an integral struture. The surfaces 162 and/or 164 o~ the blades are provided with grooves 168 which are defined by groove sidewalls 170. The grooves define a cross-sectional area and configuration substantially identical to that of the rib 26 which is to be rormed on the sidewall of the recess roove Thus, the grooves 168 are or.the order of a few thou-~ sandths on an inch in depth and their relative dimensions are '': .. exag~erated for clarity i.n the drawings. The grooves 168 may be' . formed on one.or more Or each of the surfac'es 162 or, on both . of the surfaces 162 and 164 as desired.~ In the illustrated ;- punch the grooves 168 are formed on the surface 162 of each .
- blade 160 which will define the drive wall wall 22... More than : one such groo.ve may be formed in order to rorm recesses having a plurality of ri~s as described and as illustrated in FIGS. 47 ~ .20 and 48. The grooves 168 extend from the lower edge 172 of the ~ .
... respective blade sidewalls 160 and/or 162, where the sidewalls ~oin the end surfaces 166, and extend upwardly to the extend ~ . desired. The grooves may extend fully to the.top of the blades .:.-.~ 160, l~rhere they meet the face 154 Or the punch or, may terminate ~-~; below the juncture of the blade 160 and face 154 depending on the rib confi~uration which is to be fabricated. Each of.the grooves 1s formed so that it is symmetrically disposed about a substan~

:';, tially vertical plane (i.e.. , a plane which parallels the longi-tudinal axis of the punch, one such plane being shown at 174 in FIG. 58).
, 'I ' ' . . ' 28 ~' ~

!
, ~ . . . _ . .

3~&f75 ~ ~0~737 ; 1 FIGS. 60 and 61 illustrate a punch whic}l may ~e employed to cold form t~le recess of the type shown in FIGS, 34, 35 and 36.
-~ Here, the punch is provided with the same general arrangement as ;~ descr bed above with regard to FIGS. 58 and 59. This punch, how-.. . .
ever, is lllustrated to show the configura*ion Or a modified form of groove 176 in which the rib intended to be formed has a ridge 74 (See FIG. 35) which does not parallel the recess sidewall from which it protrudes. Here, the bottom line 178 of the sidewalls 180 of the groove 176 does not extend parallel to the sidewa]l Or the blade although each groove 176 is disposed symmetrically about a vertical plane 174. The sidewalls 180 may also be in vertical planes in this embodiment.
FIGS. 62 and 63 illustrate a punch for fabricating the recess shown in FIGS. 31 and 32. This p~lnch is provided with a groovç 182 extending along its intermediate wall 184 which defines in part the punch c~re l86 and which will form the intermediate walls 18 of the recess shown in FIGS. 31 and 32. These grooves 182, as the others defined above, also are symmetrically disposed . .
along a substantially vertical plane 174.
In like manner punches may be fabricated to produce recesses of configurations like those shown in FIGS. 9, 23, 24, 39, 40-48 as well as external head configurations embodying the in~ention as suggested in FIGS. 56 and 57. The punch for forming ;: . . . . . .
one or more ribs on an externally wrenchable fastener would be defined by a socket corresponding to the shape of the head and -~ provided with one or more grooves extending along the side sur-.is faces Or the socket. It is ~elieved that the foregoing descrip-tions are sufficiently illustrative so that one of ordinary slcill in the art may now incorporate the invention in various recesses - 30 including those illustrated as well as those which are not spe-.'' .

..._.....

~ ~3 l~
- ~5~'737 cifically shoi~r. as~ ~o- c~ample, the recesses ~lo~ln in U. S~
patent No. 3,237,i:o6..
It should be u~ldcrstood that the foregoin~ description of the invention i5 intended to be illustrative thereor and that other modifications and embodiments of the invention may be appar-ent to those skilled in the art without departin~ from its spirit, :. .
. This is a divisional application of Serial No. 234,300 in the name of Frederick A. Simmons, filed August 27, 1975 and : entitled I~ROVEMENTS IN RECESSED SCREW HEADS AND DRIVERS.

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Claims (4)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A tool for mating and driving engagement with a recess in the end of a screw comprising:
a shank and a recess engaging portion formed at one end of said shank, said recess engaging portion comprising a central core and a plurality of blades radiating from said core, each of said blades defining a drive surface and a back out surface on opposite sides thereof; and a rib formed on corresponding of said surfaces of each of said blades and adjacent the lower end of each of said blades, each of said ribs extending slightly from said corresponding surfaces and extending along a direction which lies transversely to the long-itudinal axis of the driver;
each of said ribs being of a cross-sectional shape which includes a base portion and a pair of sidewalls which generally converge toward each other and meet to define the height of the ribs said rib height being of the order of a few thousandths of an inch; and each of said ribs being of generally uniform cross-sectional configuration along its length.

2. A tool as defined in claim 1 further comprising:
a second rib formed on and projecting from each of said corresponding surfaces said second rib being spaced from said first mentioned rib, each of said second ribs extending along a direction generally parallel to the first mentioned rib and being located on the blades to be within the confines of the recess when the tool is mated with the recess.

3. A tool as defined in claim 1 wherein the rib is of generally triangular cross-sectional shape.

4. A tool as defined in claim 1, wherein each of the drive and back out surfaces of each of the blades has a rib formed thereon.