US3336570A

US3336570A - Multiple element member and method of making the same

Info

Publication number: US3336570A
Application number: US342504A
Authority: US
Inventors: Tuchel Ulrich
Original assignee: Individual
Current assignee: Allied Corp
Priority date: 1963-02-06
Filing date: 1964-02-04
Publication date: 1967-08-15
Anticipated expiration: 1984-08-15
Also published as: CH425938A; DE1490757A1; DE1490757B2; NL127973C; NL6400859A; GB1047825A

Description

Aug. 15, 1967 T H L 3,336,570

MULTIPLE ELEMENT MEMBER AND METHOD OF MAKING THE SAME Filed Feb. 4, 1964 2 Sheets-Sheet l INVENTOR Uirch Tuchei ATTORNEYS U. TUCHEL Aug. 15, 1967 MULTIPLE ELEMENT MEMBER AND METHOD OF MAKING THE SAME 2 Sheets-Sheet 2 Filed Feb. IL, 1964 FFG;

INVENTOR Uirich Tuchei BY My 5 ATTORNEYS United States Patent Ofilice 3,336,570 Patented Aug. 15, 1967 28 Claims. (Cl. 339 220 The present invention relates to a multiple element member, especially a connector, and particularly to an electrical plug-type connect-or, comprising an element made of insulating material and a metallic element. The insulating member is preferably made of plastic and the metallic element serves as an electric contact piece, such as a contact blade.

Members of this type generally comprise a multiplepiece insulating body, particularly an insulating body made of two pieces. In one conventional connector of this type, the insulating body is constituted by two plastic pieces which are elongated and which are provided, at the faces at which the two pieces are brought together, with openings which, when the two pieces are in fact assembled, form a row of openings, such as slots, which pass through the insulating body. Connectors are usually made by closing the two insulating pieces about a desired number of metallic contact elements which fit into the openings formed when the two insulating pieces are brought together. The contact pieces and the openings of the insulating body are provided with suitable recesses, shoulders and/or ledges which are so arranged that the contact elernents will be firmly anchored to the insulating body, with special attention being given to so arranging the shoulders, etc., as to prevent longitudinal displacement of the contact pieces within their respective openings. Generally, the contact pieces have at least two regions of different width and/ or thickness; one of the regions projecting out of one end of the opening serves as the contact prong or blade and another region projecting out of the other end of the opening serves as an eye portion to which a lead may be soldered. These two regions will generally be made to have difierent thicknesses or widths.

Experience has shown that the above-described contact arrangement is suitable for many purposes and under many voltage conditions. One drawback, however, is that when such contacts are to be used in an atmosphere of high humidity and/ or under conditions involving the handling of extreme voltages, particularly low voltages which are subjected to exceptionally high amplification, the humidity caught and retained in the gap-like passages-which are inevitably present at the junction of the two pieces of insulating material which together form the insulating body carrying the contact elementforms electrical bridges. This, in turn, results in leakage currents flowing between the individual regions of the contact elements as well as between different contact elements carried by the same insulating body.

It is true that there exist connectors incorporating singlepiece insulating elements so that the above-mentioned difiiculties relating to the electrical insulation are avoided. Such connectors, however, have the drawback that it is difiicult to anchor the metallic contact element in the insulating body. If the metallic and insulating elements are joined to each other by means of a threadedconnection, this requires additional components and manufacturing steps. Some thought has been given to providing the contact element, if the same is in the form of a circular pin or prong, as well as the bore within which the pin is to be received, with an annular groove and to furnish an elastic ring which holds the pin within the insulating body.

This is accomplished by placing the ring in the groove and sliding the pin and ring into the bore until the ring is in axial alignment with the groove of the bore, whereupon the ring expands and partly enters the groove of the insulation, thereby securely to anchor the pin within the bore. Aside from the danger that, in the event the parts are carelessly assembled, the ring may jump out and injure the assembler, experience has shown that this type of anchoring means can not readily be used if fiat, stamped contact elements are involved. One reason for this is that the surfaces of the stamped element will first have to have the recesses milled into them, thereby requiring an additional manufacturing step, and another reason is that specially designed clamps would have to be provided in order to produce the elastic characteristics of the resilient ring.

It is, therefore, the primary object of the present invention to provide a structural entity and especially a connector which overcomes the above drawbacks, namely, to provide a connector which is suitable for use under highhumidity conditions as well as for use under conditions which require the connector to remain resistant to breakdown as well as to leakage currents, which connector, however, incorporates a unitary, i.e., single-piece, insulating element and which is susceptible to being mass-produced by manufacturing techniques which are at least as simple as those used to manufacture existing connectors.

With the above object in view, the present invention resides, essentially, in a structure in which the metallic element, i.e., the actual contact-making element if the structure is an electrical connector, is, preferably, a flat contact blade, and has at one end, preferably the thinner and/ or narrower end, at least one and preferably two opposite recesses, the contact element being held in place within the insulating element by means of a ring which is initially flat but is then deformed out of its plane into a wedge-shaped configuration such that the ring is made to enter the cut-out or cut-outs of the contact element, the thus-deformed ring being received in a suitably configured portion of the opening within which the contact element is located. In this way, the metallic element is effectively anchored in the insulating element to prevent longitudinal displacement in at least one direction, longitudinal displacement in the other direction being prevented, generally, by the provision of' interengaging shoulders with which the metallic and insulating elements are provided.

The present invention further resides in a method for making a structural entity of the above type, which method comprises the steps of first placing the metallic element in the insulating element, then slipping the retaining ring, while the same is substantially flat, over the end of the metallic element until the ring is in alignment with the lateral cut-outs with which the metallic element is formed, and finally deforming the ring out of its flat configuration thereby to impart to the ring its wedge-shaped configuration and simultaneously to draw the ring at least partly into the recesses of the metallic element.

Additional objects and advantages of the present invention will become apparent upon consideration of the following description when taken in conjunction with the accompanying drawings in which:

FIGURE 1 is a sectional view of a multiple element connector according to the present invention, the retaining ring being shown in the position it occupies after having been slipped over the lower end of the contact element (as viewed in the figure) but not yet deformed into its final configuration.

FIGURE 2 is a bottom view of the contact element and retaining ring shown in FIGURE 1.

FIGURE 3 is a fragmentary sectional view essentially similar to FIGURE 1, but showing the retaining ring in its final configuration.

FIGURES 4, 5, and 6, are plan views of modified embodiments of the retaining ring usuable in the connector according to the present invention.

FIGURE 7 is an elevational, cross-sectional view of another embodiment according to the present invention.

FIGURE 8 is a view similar to that of FIGURE 7 of a further embodiment according to the present invention.

FIGURE 9 is an elevational view with a portion of the insulating body removed, of a yet further embodiment according to the present invention.

FIGURE 10 is a view similar to that of FIGURE 9 of a still further embodiment according to the present invention.

Referring now to the drawings and FIGURE 1 thereof in particular, the same shows a connector incorporating an elongated insulating body 1 made of plastic and provided with slots 2 passing through the body. The upper end of each of the slots is provided with two opposite shoulders 3 and 4, while the lower end of each slot is provided with a wedge-shaped edge 5. Arranged within one of the slots 2 is the flat metallic contact element 6 having a wide upper end portion 7 fashioned as a contact blade, and a narrow lower end portion 8 which serves as the eye portion to which a lead may be soldered. The juncture of the upper and lower end portions results in the formation of two opposite shoulders 9 which, when the contact element is inserted into the slot 2 from above, come to sit on the shoulders 3 and 4. The lower end portion 8 of the contact element is provided with two opposite recesses or cut-outs 11 which are easily formed during the stamping operation by which the contact element 6 is made.

The retaining ring 10, shown in bottom plan view in FIGURE 2 as being of rectangular configuration, is slipped over the lower end portion of the contact element, in the direction of arrow A, until it comes to abut against the wedge-shaped opening 5. This is the position of the ring illustrated in FIGURE 1, which also shows that when the ring is in such position, it is in alignment with the cut-outs 11.

The assembly of the connector is then completed as follows: the prongs of a bifurcated tool (not shown) are placed against the middle of the two long shank portions 10a of the ring 10the areas 12 at which the ring is contacted by the prongs being indicated by phantom linesand the ring 10, which is made of any suitable material susceptible to being worked cold, is then deformed by means of a blow applied to the tool in the direction indicated by arrow A, i.e., upwardly as viewed in FIG- URE 1. This causes, firstly, the centers of the long shank portions 10a to be pressed upwardly into the middle of the wedge-shaped opening and, secondly, the short transverse end portions b to be forced toward each other so that the same will be drawn partly into the cut-outs 11 of the contact element. The ring 10 will then have assumed its final configuration, shown in FIGURE 3, in which it holds the contact element 6 firmly within the slot 2. As a result, the contact element 6 is securely anchored within the insulating element 1, longitudinal movement of the contact element 6 in downward direction being prevented by the interengagement of the shoulders 3, 4, and 9, and longitudinal movement of the contact element 6 in upward direction being prevented by the ring 10 whose engaging portions 10b are in the recesses 11 and whose now wedge-shaped portions 10a bear against the wall of the wedge-shaped receiving portion 5 of the slot 2.

Thanks to the above arrangement, there is provided a connector having a one-piece insulating body With the physical interconnection between the metallic and insulating element being such that there is no possibility for any capillary passages to form, thereby preventing the formation of leakage paths through the interior of the insulating carrier, so that the above-discussed drawbacks of the prior art connectors are avoided. Such leakage paths as tend to form at the outside of the insulation are rendered less effective by the provision of wedge-shaped protuberances 20 interposed between the slots 2.

The present invention is not limited to connectors using flat contact elements. Instead, the contact element may be a pin or a tube and both it and the opening receiving the same may have a circular or oval cross section.

The cross-sectional configuration of the central opening of the retaining ring is adapted to the cross section of the contact element. The outer cross-sectional configuration of the ring can likewise be adapted to, i.e., be similar (in the geometric sense) to, the inner cross-sectional configuration, but need not necessarily be. For example, the ring can be provided with an elongated central opening but have a circular outer configuration, as illustrated in FIGURE 4 which shows a ring 20 having a circular outer circumference but a rectangular central opening 20a.

FIGURE 5 shows a ring 30 whose outer periphery as well as whose central opening 30a are circular.

According to the embodiment of FIGURE 6, the circular ring 40, whose central opening 40a is rectangular, has a specially provided outer region 41 whose diameter is greater than that of the portion 5 of opening 2 of the insulating element 1 within which it is to be received. Consequently, when the ring 40 is struck to assume its final configuration (cf., FIGURE 3) a turned-over flange-like border is formed which fits tightly against the wall of opening 5. Such a turned-over flange can serve several purposes. For one thing, the flange is accessible from the outside and can therefore serve as a foothold for a tool introduced into the opening 5 for purposes of removing the ring. In this way, the anchoring of the contact element is a detachable one. FIGURE 7, which is taken along a plane perpendicular to the plane of FIGURE 1, shows an assembled arrangement of a contact element 6 with a retaining ring 40 of the type shown in FIGURE 6. Because the element 40 has a circular outer periphery, the opening 5 in this embodiment should also be circular. In addition, since the outer diameter of portion 41 is larger than the diameter of cylindrical opening 5, this portion 41 will be deflected downwardly, when the ring 40 is forced into opening 5', into a position opposite the recesses in element 6. Since the ring 40 is to be bent along the lines a of FIGURE 6, the metallic element 6 of this embodiment has its recesses formed in its large lateral surfaces, these surfaces being at right angles to the plane of FIGURE 7. When the ring 40 is in position, its outer edges will bear against the conical, or wedge-shaped, upper surface of opening 5'. The ring may then be formed, in a manner similar to that described above in connection with the embodiment of FIGURES l to 3, by striking the ring upwardly in the vicinity of the lines a. This will cause the ring to fold along these lines so that the long edges of opening 40a (FIGURE 6) will be moved into the recesses formed in metallic element 6. Because of the inherent resiliency of the portion 41 of ring 40, this portion will continue to bear against the cylindrical wall of opening 5'. In addition, the bending of element 40 will cause the portions of region 41 which are in line with the bending lines a to fold inwardly away from the wall of opening 5. These portions of region 41 will thus present footholds for a removal tool. Alternatively, the region 41 can be so fashioned as to bend over the other way to provide a nondetachable double-anchoring if the opening 5 of slot 2 is provided with an inwardly extending ring 18 (FIGURE 1) behind which the flange is formed. The retaining ring itself can thus serve to provide a fastening which prevents movement of the contact element in both directions. This type of anchoring is, however, generally not needed if the contact element is, as described above, provided with shoulders 9 which seat on shoulders 3 and 4 of the insulating body 1.

Such an arrangement is shown in the cross-sectional View in FIGURE 8 and includes a ring 40 which is initially identical in form to the ring shown in FIGURE 6. This ring is provided with a region 41 which is bent upwardly in a manner illustrated prior to insertion into the ring-receiving opening in insulating body 1. Insulating body 1 is provided with an inwardly extending ring 18 of the type described above in connection With FIGURE 1. Since this ring 18 is of the same plastic material as body 1 and is relatively thin, the ring 40 can easily be forced therepast and into position opposite the recesses provided in metallic contact element 6', this contact element differing from the element 6 in that it is not provided with shoulders 9. As is the case for the embodiment of FIGURE 7, the recesses in the element 6' are also formed in the large lateral surfaces of that element. The outer ends of region 41 will bear against the conical surface of the ring-receiving opening-so that, when the ring 40 is upstruck in the manner described above, the ring will be prevented from moving upwardly as a whole and will therefore deform in the manner illustrated so that the long sides of openings 40:: move into the recesses provided in contact element 6. The resulting assembly will have the configuration shown in FIGURE 8, wherein the upper extremity of region 41 prevents upward longitudinal movement of contact element 6' and the lower extremity of region 41, which is opposite ring 18, prevents downward movement of the contact element.

The above-described arrangement involving the use of the ring of FIGURE 6, which prevents movement of the contact element in both directions, is particularly useful when the contact element does not pass entirely through the insulating element, i.e., when the contact element is arranged in a blind bore of the insulating element.

The lines a in FIGURES 4 and 6 show the position of the crest of the retaining ring, after the same has been bent into the wedge shape, with respect to the central opening thereof. This crest can be parallel or at right angles to the long axis of the rectangular central opening.

FIGURE 9 is an elevational view of another arrangement according to the present invention in which portion of body 1 is removed to show the other parts of the assembly. The assembly includes a contact element 6 of the type shown in FIGURES l and 3, an insulating body 1 having an opening 5' provided with a conical receiving portion, and a retaining ring 20 of the type shown in FIGURE 4. The retaining ring 20 is inserted into the opening 5' with its opening 20a in alignment with the recesses provided in the narrow lateral edges of contact element 6. When this retaining ring is in its flat condition, its outer periphery bears against the conical portion of opening 5' so that, when the ring is up-struck along lines a, the ring will be prevented from moving upwardly as a whole and will become deformed in the manner illustrated so that the short edges of opening 20a willbe urged into the recesses provided in element 6, these recesses being indicated by phantom lines.

The same procedure is followed in the assembly of the embodiment of FIGURE 10, which is a view similar to that of FIGURE 9 and in which the contact element 6" has a tubular portion 7' and a round pin portion 8' provided with an annular recess, as indicated by phantom lines. When the element 30, which is shown in plan view in FIGURE 5, is upstruck the portions of opening 30a which are perpendicular to the line along which the retaining ring is bent will be forced into the annular recess in portion 8.

The present invention provides a number of advantages insofar as manufacturing techniques are concerned. For example, a single insulating body 1, which may be made by injection, casting, pressing or other molding processes, can have a number of contact elements arranged on one side, all of which are inserted into respective slots 2 in one operation. The means for introducing the retaining rings are arranged on the opposite side. These rings can be inserted eitherv successively or simultaneously. The inserted rings can then be deformed, either consecutively or simultaneously, by a suitable press or striker mechanism, or set of presses and striker mechanisms. In this way the entire connector can be easily assembled by machine. This, too, renders the connectors susceptible for use as miniature components, the manual assembly of which requires, a very high degree of accuracy, generally not-realizable by other than highly skilled labor.

The present invention is not limited to the precise details described above. For example, the cut-outs 11 can be differently configured to meet the needs of the situation; for example, they can be in the form of notches. Also, it is possible to impart the wedge-shaped configuration to the retaining ring by striking the same at but one point. Furthermore, the metallic contact element can be held in place by two retaining rings, one at each end. While this would require some additional manufacturing steps, the same may be justified if the contact element is made of very expensive material so that the saving of such materialby the omission of the shoulder arrangement, for example-would more than compensate for the provision of the two retaining rings.

Nor is the present invention limited to electrical connectors, since the above-described retaining ring arrangement may be used generally to anchor a metallic element in an insulating or plastic element. The anchoring may be used to avoid the difficulties incident to mounting the metallic element in the plastic element while the latter is still in deformable state.

It will be understood that the above description of the present invention is susceptible to various modifications, changes, and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

What is claimed is:

1. A structural entity comprising, in combination: a one-piece element made of insulating material provided with an opening; a metallic element arranged in said opening; and a thin retaining ring surrounding said metallic element and securing said elements to each other; said opening of said insulating element having a receiving portion and said metallic element having at least one recess; said retaining ring having at least one substantially flat portion lying in a plane transverse to the longitudinal axis of said opening and extending at least partly into said at least one recess of said metallic element, and a bent portion having a V-shaped cross section in at least one plane parallel to such longitudinal axis, said bent portion being disposed in said receiving portion of said opening, thereby to prevent movement of said metallic element, relative to said insulating element, in at least one direction.

2. A structural entity comprising, in combination: a one-piece element made of insulating material provided with an opening; a metallic element arranged in said opening; and a deformable retaining ring surrounding said metallic. element and securing said elements to each other; said opening of said insulating element having a receiving portion and said metallic element having at least one recess; said retaining ring, which, while in its originally flat condition, was placed into said opening to be in alignment with said recess and was thereafter deformed out of its plane to assume a wedge-shaped configuration, having a portion which is in said receiving portion of said opening and another portion which is at least partly in said recess of said metallic element, thereby to prevent movement of said metallic element, relative to said insulating element, in at least one direction.

3. The combination defined in claim 2 wherein said receiving portion of said opening has a wedge-shaped edge.

4. The combination defined in claim 2 wherein said metallic element is elongated in a longitudinal direction and has a first cross section throughout a portion of its length and a different cross section throughout another portion of its length.

5. The combination defined in claim 4 wherein said metallic element is provided with at least one shoulder and wherein said insulating element is provided with at least one shoulder; said shoulder of said metallic element seating on said shoulder of said insulating element thereby to prevent longitudinal movement of said metallic element, relative to said insulating element, in direction opposite to the direction in which relative longitudinal movement is prevented by said retaining ring.

6. The combination defined in claim 2 wherein said retaining ring is made of a material which is deformable while said ring is cold.

7. The combination defined in claim 2 wherein said metallic element is a flat elongated element.

8. The combination defined in claim 7 wherein said metallic element is a stamped element.

9. The combination defined in claim 7 wherein said opening extends through said insulating element and is slot-shaped throughout at least a portion of its length.

10. The combination defined in claim 7 wherein the inner peripheral configuration of said ring is similar to the outer cross-sectional configuration of said metallic element at the region where said ring is in alignment with said recess.

11. The combination defined in claim 7 wherein said metallic element is a round pin throughout at least a portion of its length.

12. The combination defined in claim 7 wherein said metallic element is tubular throughout at least a portion of its length.

13. The combination defined in claim 7 wherein said ring is rectangular.

14. The combination defined in claim 7 wherein the inner and outer peripheral configuration of said ring are different from each other.

15. The combination defined in claim 7 wherein said ring has an outer dimension greater than the size of said receiving portion of said opening and is provided with a turned-over flange portion at least a part of which intimately engages the surface of said receiving portion.

16. The combination defined in claim 15 wherein said insulating element is provided with an inwardly extending portion, said flange portion being folded behind said lastmentioned portion.

17. The combination defined in claim 2 wherein said metallic element is an electrical contact.

18. The combination defined in claim 2 wherein said metallic element is a flat contact blade.

19. A connector comprising, in combination: a onepiece element made of insulating material and provided with an opening; an elongated metallic contact element extending through said opening; and a thin retaining ring surrounding said contact element and securing said elements to each other; said opening of said insulating element having a receiving portion and said contact element having a pair of lateral recesses arranged opposite each other; said retaining ring having two substantially flat portions lying in a plane transverse to the longitudinal axis of said opening and each extending at least partly into a respective one of said pair of recesses of said contact element, and a bent portion having a V-shaped cross section in at least one plane parallel to such longitudinal axis, said bent portion being disposed in said receiving portion of said opening, thereby to prevent longitudinal displacement of said contact element, relative to said insulating element, in at least one direction.

20. A connector comprising, in combination: a onepiece element made of insulating material provided with an opening; an elongated metallic contact element extending through said opening; and a deformable retaining ring surrounding said contact element and securing said elements to each other; said opening of said insulating element having a receiving portion and said contact element having at least one lateral recess; said retaining ring,

which, while in its originally fiat condition, was placed into said opening to be in alignment with said recess and was thereafter deformed out of its plane to assume a wedge-shaped configuration, having a portion which is in said receiving portion of said opening and another portion which is at least partly in said recess of said contact element, thereby to prevent longitudinal displacement of said contact element, relative to said insulating element, in at least one direction.

21. A connector as defined in claim 20 wherein the interior and exterior peripheral configurations of said ring are geometrically similar to the cross-sectional configuration of said contact element at the region thereof at which said contact element is provided with said recess.

22. A connector as defined in claim 20 wherein the interior and exterior peripheral configurations of said ring are different from each other.

23. A connector as defined in claim 22 wherein the outer peripheral configuration of said ring is circular and the inner peripheral configuration of said ring is elongate.

24. An electric connector comprising, in combination: a one-piece element made of insulating material and provided with a plurality of openings; a plurality of elongated metallic contact elements extending through said openings, respectively; and a plurality of deformable retaining rings each surrounding a respective contact element and securing the same to said insulating element; each opening of said insulating element having a receiving portion and each contact element having a pair of lateral recesses arranged opposite each other; each retaining ring, which, while in its originally fiat condition, was placed into a respective opening to be in alignment with the pair of recesses of the respective contact element and was thereafter deformed out of its plane to assume a wedgeshaped configuration, having a wedge-shaped portion which is in the receiving portion of the respective opening and two opposite engaging portions which are at least partly in the two recesses of the respective contact element, thereby to prevent longitudinal displacement of said contact elements, relative to said insulating element, in at least one direction.

25. A method of making a structural entity, comprising the steps of: providing a one piece element made of insulating material and having an opening; placing a metallic element having at least one recess in said opening; thereafter placing a retaining ring, while the same is substantially flat, about said metallic element and into said opening to be in alignment with said recess of said metallic element; and thereafter deforming said ring out of its fiat configuration to impart to said ring a wedgeshaped configuration, thereby simultaneously to draw one portion of said ring at least partly into said recess of said metallic element.

26. A method of making a connector, comprising the steps of: providing a one-piece element made of insulating material and having an opening; placing an elongated metallic contact element having a pair of lateral recesses arranged opposite each other in said opening; then placing a retaining ring, while the same is substantially fiat, about said contact element and into said opening so that the ring lies in a plane common to said two recesses; and thereafter deforming said ring out of its fiat configuration to impart to said ring a wedge-shaped configuration, thereby simultaneously to draw two engaging portions of said ring at least partially into said two recesses of said contact element.

27. A method as defined in claim 26 wherein said ring is deformed by the application of a striking blow to two diametrically opposite portions of said ring, the line joining said two last-mentioned portions of said ring being at right angles to the line joining said two engaging portions of said ring.

28. A method of making an electric connector, comprising the steps of: providing a one-piece element made of insulating material and having a plurality of openings; disposing a plurality of contact elements, each having a pair of lateral recesses arranged opposite each other, in said openings; then simultaneously placing each of a plu rality of retaining rings, while each is substantially fiat, about a respective one of said contact elements and into the respective openings so that each ring lies in a plane common to the two recesses of its respective contact element; and thereafter simultaneously deforming each of said rings out of its flat configuration to impart to each respective ring a wedge-shaped configuration, thereby simultasneously drawing two engaging port-ions of each ring at least partly into the two recesses of its respective contact element.

References Cited UNITED STATES PATENTS Goldberg.

Gruber 29-520 Richardson.

Gaubert et al.

Wilson 151-30 Carlson.

Bingham 29520 X Kelly 339-217 MARVIN A. CHAMPION, Primary Examiner. PATRICK A. CLIFFORD, Examiner.

Claims

1. A STRUCTURAL ENTITY COMPRISING, IN COMBINATION: A ONE-PIECE ELEMENT MADE OF INSULATING MATERIAL PROVIDED WITH AN OPENING; A METALLIC ELEMENT ARRANGED IN SAID OPENING; AND A THIN RETAINING RING SURROUNDING SAID METALLIC ELEMENT AND SECURING SAID ELEMENTS TO EACH OTHER; SAID OPENING OF SAID INSULATING ELEMENT HAVING A RECEIVING PORTION AND SAID METALLIC ELEMENT HAVING AT LEAST ONE RECESS; SAID RETAINING RING HAVING AT LEAST ONE SUBSTANTIALLY FLAT PORTION LYING IN A PLANE TRANSVERSE TO THE LONGITUDINAL AXIS OF SAID OPENING AND EXTENDING AT LEAST PARTLY INTO SAID AT LEAST ONE RECESS OF SAID METALLIC ELEMENT, AND A BENT PORTION HAVING A V-SHAPED CROSS SECTION IN AT LEAST ON PLANE PARALLEL TO SUCH LONGITUDINAL AXIS, SAID BENT PORTION BEING DISPOSED IN SAID RECEIVING PORTION OF SAID OPENING, THEREBY TO PREVENT MOVEMENT OF SAID METALLIC ELEMENT, RELATIVE TO SAID INSULATING ELEMENT, IN AT LEAST ONE DIRECTION.