US3115379A

US3115379A - Electrical connector

Info

Publication number: US3115379A
Application number: US155764A
Authority: US
Inventors: William H Mckee
Original assignee: United Carr Fastener Corp
Current assignee: United Carr Fastener Corp
Priority date: 1961-11-29
Filing date: 1961-11-29
Publication date: 1963-12-24
Anticipated expiration: 1980-12-24

Description

Dec. 24, 1963 w. H. Mcm-:E 3,115,379

ELECTRICAL CONNECTOR Filed Nov. 29, 1961 4 Sheets-Sheet 1 l` I'g l'l'l I j; j 5J l Z0 l 13 z l i 4' 2c 7c I6 I? F' 1 FEI. 2

5 8 5 3 20 le I7 8 Z 3 201W| l5 /I'S \l8 'Hl l 'o 5 4 6 ZL i 17 *iig-7 @j Dec. 24, 1963 w. H. MGKEE 3,115,379

ELECTRICAL CONNECTOR Filed Nov. 29, 1961 4 Sheets-Sheet 2 HIHIH. l1. 4,/ 9 M3 zo] la Zij Fi H .14 1v1/etz for.'

, /x/ML/AM A. fifa/(iff 5g: chimlb Dec. 24, 1963 w. H. MGKEE ELECTRICAL CONNECTOR 4 Sheets-Sheet 3 Filed NOV. 29, 1961 I aven to r Dec. 24, 1963 w. H. MGKEE 3,115,379

ELECTRICAL CONNECTOR Filed NOV. 29, 1961 4 Sheets-Sheet 4 In veno fwn/,4M H MaX/ff United States Patent O 3,115,379 ELECTRICAL CNNECTGR William H. McKee, West Covina, Calif., assignor to United-Carr Fastener Corporation, Boston, Mass., a corporation of Delaware Filed Nov. 29, 1961, Ser. No. 155,764 4 Claims. (Cl. 339-47) The present invention relates to an electrical circuit connecting device and more particularly it relates to an improved contact element structure for electrical connecting devices.

Most electrical connectors utilize complementary pairs of dissimilar contact elements. Normally one unit of each pair is provided with female type contact elements or sockets adapted to receive male type elements or prongs of the other unit of the pair. Such electrical connectors require the manufacture of separate and distinct connecting implements or elements for each complete connection. This entails the manufacture of the separate components and the stocking by distributors of different types of elements for each type of connector.

The electrical connectors of the present invention are provided with pairs of prongs either of identical shape or mirror images when facing the outer ends of interengageable pairs. Only one ty'pe of element need be blanked in manufacturing, thus, facilitating manufacture of such components.

The `connectors of the present invention further embody features of construction providing large area wiping interfacial contact areas upon engagement of mating units. These large wiping contact areas assure low contact resistance and preclude poor high resistance contact resulting from an insulating iilm, dust or small area engagernent.

Further in accordance with one aspect of the present invention, universal contact elements are formed of bifurcated resilient metal stampings, such `as phosphor bronze, having their fork-defining prongs offset in two directions in relation to the :cent-ral line of the element and effective to engage the mating .element in edge contact that fiexes the prongs in both directions to provide resilient contact-making engagement.

Another aspect of the present invention resides in the overlapping interfacial areas of the fork-deiining prongs of each of the luniversal contact elements.

It is accordingly a general object of the present invention to provide an improved electrical connector wherein the interengaging elements are identical in construction.

It is a further object of the present invention tol provide an improved electrical connector wherein the prongs or interengaging elements are mirror images of each other when facing the outer ends of interengageable pairs and are formed from the same blank material.

It is an additional object of the present invention to provide an improved electrical connector device having an improved prong or electrical contact that provides a large wiping electrical contact area to the mating connector.

A further object of the present invention is to provide an improved electrical connecting device having a novel electrical Contact design wherein any one contact may be electrically mated with yany other connector.

An additional object of the present invention is to provide an improved electrical connecting device having improved electrical contacts, said contacts being constructed such that they provide universal joint action when connected to facilitate easy insertion and withdrawal of the contacts with relation to each other.

Still another object of the present invention is to provide an improved contact construction wherein prongs 3,115,379 Patented Dec. 24, 1963 ICC engage on their edge portions, they are spaced and flexed in two directions in relation to the plane of 'the prongs, and yet no reliance is placed upon the presence of a bevel on the prongs.

A further object of the present invention resides in the provision of a universal electrical connecting element for printed circuit boards having indexing members thereon for convenience in assembly.

It is still another object of the present invention to provide an improved electrical connecting device for printed circuit boards that is easily mounted thereon and that provides an easy interengagement with mating connectors from mating circuits so that easy and convenient insertion and withdrawal of the circuits and connectors may be realized.

Yet another object of the present invention is to provide an improved bifurcated contact element wherein the prongs tiex in two directions to provide edge-engaging lo-w-resistance contact making pressure.

The novel features which I believe to be characteristic of my invention are set forth with particularity' in the appended claims. My invention itself, however, together with further objects and advantages thereof, will best be understood by reference to the following description taken in connection with the accompanying drawings, in which:

FIGURE l is a top plan view of one form of the connector element of the present invention shown unmounted. It should be appreciated that the connector element shown may be mounted in any suitable insulating receptacle or, for example, on a printed circuit board;

yFIGURE 2 is a side view of a mating connector element showing in detail the depending legs or electrical contacts to facilitate mounting of the element on a printed circuit board;

FIGURE 3 is a side view of -a connector element of FIGURE 1 showing an element especially adapted for mounting in a suitable insulating receptacle and provided with a soldering lug or wire wrap terminal at one extreme thereof;

FIGURE 4 is a bottom plan view of a connector element identical to that shown in FIGURE 2 but rotated 90 to show it in mating relationship to the contact of FIG- URE 3;

FIGURE 5 is a cross-sectional view of the contact elements shown in FIGURE 3 taken along lines 5-5 of FIGURE 3, showing the overlapping interfacial areas in greater detail;

FIGURE 6 is an end view of the connector shown in FIGURE Z taken from the contact element end showing in greater detail the overlapping relation of the contact elements;

FIGURE 7 illustrates the stamped blank metal piece from which the connector elements, such as those shown in FIGURES 3 and 4, are formed;

FIGURE 8 illustrates the stamped blank metal piece from which the connector elements, such as those shown in FIGURES 1 and 2, are formed;

FIGURE 9 is an end view of the metal blank shown in FIGURE 7, taken from the contact element end;

FIGURE 10 is a fragmentary end view of the metal blank shown in FIGURE 8, taken from the contact element end;

FIGURE 11 is a perspective view of a pair of electrical connector elements constructed in accord with one modication of the present invention, the elements being shown in mating interengaging relationship;

FIGURE 12 is a cross-sectional view through lines 12-12 of FIGURE 11 illustrating the large interfacial contact area of the interengaging contacts;

FIGURE 13 is a perspective view of a pair of electrical connector elements according to another mode of the present invention, the elements being shown in interengaging relationship;

yFIGURE 14 is a cross-sectional view through lines 14-14 of FIGURE 13 again illustrating the large electrical contact area presented by the contact elements of the present invention;

'FIGURE 15 illustrates the contacts of FIGURE 13 in interengaging relationship and as mounted in the printed circuit board members;

FIGURE 16 is `a perspective view of another embodiment of the present invention illustrating the connector element as shown in FIGURE 2 but with rotated or twisted electrical contact elements;

FIGUR-E 17 is an end view of the electrical connector element shown in perspective in FIGURE 16I taken from the contact element end;

FIGURE 18 is a perspective View of a pair of electrical connector elements, as illustrated in FIGURE 16, shown `in mating, interengagin-g relationship;

IFIGURE 19 is a cross-section view through the contact elements of the type shown in FIGURE 18 with the contact elements in interengaging relationship, illustrating the large interfacial contact area;

FIGURE 20 is a perspective view of a pair of interengaging electrical connector elements illustrating the connector element as shown in FIGURES 3 and 4 but with rotated or twisted electrical contact elements;

lFIGURE 2.1 is a cross-sectional view through lines 21-21 of FIGURE 20 illustrating the large electrical contact area between the interengaging contact elements;

FIGURE Z2 is a perspective Viewl of a pair of interengaging electrical connector elements illustrating another modication of the present invention; and

FIGURE 23 is a cross-sectional View taken through lines 423--23 of FIGURE 22 showing the electrical contact area presented between the interengaging contact ele-ments.

Referring now more particularly to 4FIGURE 1 of the drawings, there is shown an electrical connector element, indicated generally at 1. The connector element 1 is preferably stamped and formed from a sheet of electrically -conductive brass material although it should be understood that any suitable material having the requisite electrical and mechanical characteristics would be satisfactory `for the connector elements.

As shown in FIGURES 7 and 9, the connector element v1 is initially stamped out of a hat metal sheet which process contributes to manufacture of the element on a high volume basis. The originally stamped connector element 1 is provided with a soldering lug or wire wrapping post 2 at one end thereof and is bifurcated at the other end thereof to provide a pair of spaced apart

contact elements

3 and 4. The spaced apart

contact elements

3 and 4 have substantially hat 'facing

surfaces

7a and 7b, respectively, the surfaces being so shaped to provide a large electrical contact face to interengaging contact elements.

During the stamping operation a small portion of the metal at the base of the slot 6' is cut away from the remainder of the metal stamping at either side. The portion 5 is then bent or formed to a position displaced 90 from the plane in which it originally lay to form a Y lug '5, which lug forms a stop or positioning member for the connector element 1 so that said element may be inserted within an insulating body (not shown) in a casual Y fashion and always come to rest in a position that allows l tion the connector element 1 may be twisted slightly to permit the recesses 8 and 161 to engage said ilange section to thereby tix the element 1 with respect to the insulating body.

The

contact elements

3 and 4 are then deformed to the positions show-n therefor in FIGURES 1 and 3. As is illustrated,

contact elements

3 and 4 are each bent slightly outwardly away from the central longitudinal plane of the connector element 1 to a position where the inner planar yfaces 11 and 12 of said

elements

3 and 4 lie in substantially the same fvertical plane. The elements 3 and `4 are bent slightly inwardly, toward the central axis of the connector element 1 as illustrated in FIGURES 3 and 5 so that an overlapping area, indicated generally at 14, is presented wherein the inner marginal area of each of the faces 11 and 1.2 of the

contact elements

3 and 4, respectively, are in contact along substantially the length of the contact elements.

The electrical connector elements 1, illustrated in FIG- U-RES l and 3, are of a design such that when one element is placed in end-to-end, contact element-facing relationship with one another connector element, the

contact elements

3 and 4 will interengage with relative ease and provide a good electrical connection between said pair of connector elements. It will be readily seen that the contact elements 3 and `4 must be urged slightly apart when interengaging with a second pair of contact elements. When a pair of

contact elements

3 and 4 are interengaged in electrical connecting relationship, the inner planar `faces 11 and 12 do not overlap. It should be observed that the material fromy which the connector elements is manufactured should have a yield point at least in excess of that force required to urge the

elements

3 and 4 slightly apart when in electrical engagement with another pair of elements so that when the pair of connector elements are disengaged, the

contact elements

3 and 4 will return to their original overlapping positions, as deiined above.

A modied connector element, as shown generally at 1S in FIGURES 2 and 4, is especially adapted vfor use with printed circuitry. The connector element 15 may also be stamped from a sheet of material having suitable electrical and mechanical characteristics.

The stamped connector element 15 has a body portion 13 and a pair of

legs

16 and 17 depending from said body portion `13. The element 15 is slotted at 1S on the opposite half thereof to define a pair of contact elements 2t) and 21. The facing surfaces 7c and 7d of contact elements 2t) and 21 are substantially flat along substantially the length of the contact to thereby provide a large electrical `Contact area to similarly shaped contact elements.

The contact elements 2t! and 21 are deformed after stamping to the positions shown in FIGURES 2 and 4. As shown, the contact elements 2i) and 21 are each bent slightly out-wardly-near their base positions-away from the central longitudinal plane of the connector element 15 to a position where the inner planar faces 22 and 23 of the elements lie in substantially the same plane. The contact elements Ztl and 21 are then bent slightly inwardly toward the central axis of the connector element 15, as illustrated in 'FIGURES Z and 4, so that an overlapping area, indicated generally at 24, is presented wherein the inner marginal area `of each of the

faces

23 and 24 of the

contact elements

20 and 21, respectively, is in contact along substantially the length of the contact elements.

The

contact elements

1 and 15 illustrated in FIGURES 1 and 2 are illustrated in FIGURE 11 in mating, interengaging relationship in which relationship an electrical path is completed between said contact elements. The

contact elements

1 and 15 are shown of themselves and are illustrated as mounted in the conventional insulating body. It should be understood that the contacts in use will always be mounted .in a receptacle of some form to facilitate their use in the most convenient form. The combination of

contact elements

1 and 15 of FIGURE l1 would, for example, electrically connect a conventional circuit with a printed circuit. The contact is preferably mounted on a printed circuit board, as shown generally in FIGURE 15, with the depending

legs

16 and 17 making electrical Contact with the circuit leads of the printed circuitry. The contact 1 is preferably mounted, for example, in a conventional insulating base or plug with wire leads extending from the soldering lug or wire wrap post 2.

FIGURE 12 is a cross-sectional view through line 12-12 of FIGURE 11 which is the contact-engaging area of the

contact elements

1 and 15. As illustrated, the contact elements 3 and 4' of the contact 1 engage the contact elements and 21' of the contact 15 in intimate electrical connecting relationship. The

contact elements

3', 4', 20 and 21 are the same as

Contact elements

3, 4, 20 and 21 as shown in FIGURES 1 and 2 except that they `are bent away from the body plane in opposite directions therefrom. It should be understood, of course, that it is immaterial in which direction the contact elements are bent away from the body plane. The contact elements 3', 4', Ztl' and 21', when interengaged, are spread slightly. The spreading action of the contact elements when engaged with a mating pair of contact elements gives rise to a vise effect acting on the mating elements. This mechanical vise effect enhances the mechanical interference between the mating contacts and ha'.- the net effect of facilitating the mechanical interconnection thus tending to sustain the connection and inhibit any casual disconnection of the contacts. It should be understood that a plurality of contacts may be mounted on the same circuit board or within the same insulating body in mating relationship to provide a convenient receptacle having facilities for a plurality of interconnecting electrical circuits.

It will be noted from the cross-sectional view of FIGURE 12 that a large interfacial electrical contact area is presented between the contact elements 3', 4', 20' and 21', which contact elements are made in accord with the present invention. The large electrical contact area of the interengaged contact elements of the present invention is in contradistinction to the contact area present on the connecting devices presently commonly employed. It will be noted that the present connecting devices provide a line contact or point contact between the contact elements. At best, the present connecting elements may provide facial contact of a flat element (in the case of the male-female type contact), but normally such connecting devices have the disadvantage of being dissimilar in construction as pointed out above. The at facing surfaces 7fz-bcd of the contact elements further provide the same contact area along substantially the entire distance of the interengaging contact elements. It is apparent that the large contact area between the contact elements gives rise to an inherently efficient electrical contact. Contact resistance is considerably reduced and the probability of a foreign, non-conducting substance shorting out the contact is likewise reduced with the net result that a more reliable and efficient contact is made.

FIGURES 13 and 14 are illustrative of the interengaging relationship of two identical contacts 15 of 111e present invention. It will be observed that one-half of the total surface area of the contact elements, per unit of length thereof, is in electrical contact with the mating Contact elements. Such relatively large contact areas provide a highly efficient electro-mechanical connection between connectors manufactured in accord with the present invention. FIGURE 15 illustrates a connector element 15 of the type shown in FIGURES 2 and 4 as mounted on a conventional printed circuit board. Each of the connector elements 15 is shown mounted in a board 25. As shown, the

legs

16 and 17 of each of the Connector elements 15 are inserted into and extend through each of the circuit boards to protrude -a slight 6 distance beyond the opposite surface of the board. Each of the

legs

16 and 17 of the connector element 15 perforates and extends through an electrically conductive printed ribbon or circuit member to establish preliminary electrical contact therewith. A deposit of solder 2.7 or some other suitable electrically conductive material that will establish and maintain a positive ele-ctrical connection between the

legs

16 and 17 and the ribbon element 26 is placed about the protruding portion of the

legs

16 and 17 to thereby electrically and mechanically connect the ribbon 26 and

legs

16 and 17. The connecting elements 15 are positioned on the circuit board 25 in a position such that the contact elements 20' and 21 of each of the connector elements 15 will extend beyond the edge 28 of each of the boards 25, so that the contact elements are in a position to interengage with mating contact elements of the connector elements to be joined therewith. The abutting ends 28 of the printed circuit boards 25 serve as a positive stop to prevent insertion of one pair of contact elements into the mating pair too great a distance, which would result in damage to the elements. It should be observed that a conventional insulating body (not shown), into which connecting elements 1 as shown in FIGURES 1 and 3 may be inserted, would serve as the stop or positioning member to provide for proper engagement of the mating contact elements.

Another modification of the present invention is illustrated in FIGURES 16 through 19. A connector, indicated generally at 30, is comprised of the same body portion 13 as the connector elements shown in FIGURES 2 and 4, and depending

legs

16 and 17 for the purpose of attaching the connector to a printed circuit board, as shown generally in FIGURE 15.

Contact

elements

31 and 32 are of the same general type and outline configuration as the contact elements 2t? and 21 of connector element 15, except that the

elements

31 and 32 are twisted with respect to the main body portion 13 of the connector element 30.. The

contact elements

31 and 32 are each disposed in. -a separate plane, parallel to each otherthe same as disclosed with regard to the elements of connector 15-each of the planes of the

elements

31 and 32 being rotated with respect to the plane of the main body portion 13 of the connector element 30.

FIGURE 17 is an end view of the connector element 3i) shown in FIGURE 16 taken from the contact element end of said connector. FIGURE 17 illustrates more clearly the twisted, overlapping relationship of the

contact elements

31 and 32. It should be understood that the connector elements 30 of FIGURE 16 may be provided with the prong-shaped soldering lug or wire wrap post for connection of the wire leads to the element 30 rather than the body 13 and depending

legs

16 and 17 as shown therein. Such construction is shown for illustrative purposes only.

FIGURE 18 illustrates a pair of connector elements 3), such as shown and described in conjunction with FIG- URE 16, in interengaging mating relationship..

FIGURE 19 is a cross-sectional view through the interengaging contact element area of a pair of interengaging connector elements 30, of the general type shown in FIGURES 16 through 18. FIGURE 19 again illustrates the relatively large electrical contact area presented by the

interengaging contact elements

31 and 32 of the present invention.

FIGURE 20 illustrates another embodiment of the present invention. A connector element, indicated generally at 34, has a connecting post or lug 35 to which the wire leads to be electrically and mechanically connected to said post are soldered, wrapped or fastened by some other suitable means. Oppositely disposed recesses 36 are provided within the body portion of the connector 34. The recesses 36 are employed to assist in positioning the connector element 34 within a suitable insulating body (not shown). It should be understood that said recesses 36 may engage a flange portion within said insu- 7 lating body and be locked thereto by twisting over said flanges to non-removably position said element 34 within the body. An upraised lug 37 is provided on the connector element to longitudinally position the connector element 34 within the insulating body (not shown). The connector element 34 may be insertedin one method of assemblyinto a slot provided in an insulating body. The lug 37 would then engage an abutting portion within the slot of the insulating body, which abutting portion Would serve to prevent the connector element 34 from passing completely through the slot in the insulating body. The lug thus, in an insulating body as generally described, would serve to position the connector element 34 Within said insulating body so that the

contact elements

38 and 39 of said connector element 34 would project beyond the insulating body the desired amount and in such position be adapted for interengagement with a similar connector element to provide an electrical connection between two electrical circuits. The

contact elements

38 and 39 of each of the connector elements 34, respectively, are disposed in a separate plane parallel to each other but rotated from the plane of the main body portion of the connector elements 34.

FIGURE 21 is a cross-sectional view taken along line 21-21 of FIGURE 20 and is illustrative of the relatively large electrical contact area presented by the

interengaging contact elements

38 and 39, respectively.

Another modiiication of the present invention is shown in the embodiment of FIGURE 22. In this modication the connector elements, indicated generally at 40, are each provided With a pair of

contact elements

41 and 42. The

contact elements

41 and 42 are each bent away from the main body portion of the connector elements 40 in stepped fashion such that each of said contact elements is disposed in a separate plane spaced from, but parallel to, the plane of the main body portion of the connector element 40. Each of the

contact elements

41 and 42 of the connector elements 40 has a rounded portion 45 adjacent the end of each of said contact elements. When the

contact elements

41 and 42 of a pair ot' connector elements 40 are in interengaging relationship, the rounded portions 45 of each of the contact elements, respectively, will be adjacent each other, lying in the sarne general plane of contact. This feature of construction gives rise to a camrning action between the pairs of contacts to facilitate engagement and disengagement of the contacts without damage to the contact elements or their related structure.

FIGURE 23 is a cross-sectional View taken through lines 23-23 of FIGURE 22. The large electrical contact area of the identical mating connector elements 4i) occurs at the plane of intersection of the rounded portion 45 of the

contact elements

41 and 42, respectively.

While I have shown and described specific embodiments of the present invention, it will, of course, be understood that other modifications and alternative constructions may be used without departing from the true spirit and scope of this invention. I, therefore, intend by the appended claims to cover all such modications and alternative constructions as fall within their true spirit and scope.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electrical connector comprising a pair of contact members, each of said members having a body portion lying in a predetermined plane and having a bifurcation to provide a pair of spring contact elements extending from said body portion, each of said elements having inner and outer parallel planar broad surfaces and top and bottom edge surfaces between said broad surfaces, said elements of each pair being offset laterally of each other to dispose the inner broad surface of each element in substantially the same plane, said elements of each pair being positioned with portions of said inner broad surfaces in overlapping relation, lead means at the outer ends of said elements for effecting electrical engagement of the contact elements of each pair in an end to end direction, said elements of each pair expanding during said interengagement to contact said other pair of e1ements under spring tension.

2. An electrical connector as dened in claim 1 in which said planar broad surfaces of each pair of contact elements are disposed in parallel relation to said plane of said respective body portion from which said pair extends.

3. An electrical connector as delined in claim 2 in which said planar broad surfaces of each pair of contact elements are disposed in angular relation to said plane of said respective body portion from which said pair extends.

4. An electrical connector comprising a pair of contact members, each of said members having a body portion lying in a plane normal to the plane of said other body portion, each of said body portions having a bifurcation to provide a pair of spring contact elements extending from said body portion, each of said elements having inner and outer planar broad surfaces and top and bottom edge surfaces between said broad surfaces, said elements of each pair being offset laterally of each other to dispose the inner broad surface of each element in substantially the same plane, said elements of each pair being positioned with portions of said inner broad surfaces in overlapping relation, lead means at the outer ends of said elements for effecting electrical engagement of the contact elements of each pair in an end to end direction, said elements of each pair expanding during said interengagement to engage an edge surface of each element of one pair with said inner planar broad surface of each element of said other pair.

References Cited in the ile of this patent UNITED STATES PATENTS 2,125,816 Reynolds Aug. 2, 1938 2,762,022 Benander et al Sept. 4, 1956 2,779,011 Deakin Jan. 22, 1957 2,953,766 Clewes Sept. 20, 1960 2,994,056 Fox July 25, 1961 3,011,143 Dean Nov. 28, 1961 3,012,221 Deakin Dec. 5, 1961 FOREIGN PATENTS 218,200 Switzerland Apr. 16, 1942 538,801 Great Britain Aug. 18, 1941 1,187,074 France Mar. 2, 1959 1,247,715 France V Oct. 24I 1960

Claims

1. AN ELECTRICAL CONNECTOR COMPRISING A PAIR OF CONTACT MEMBERS, EACH OF SAID MEMBERS HAVING A BODY PORTION LYING IN A PREDETERMINED PLANE AND HAVING A BIFURCATION TO PROVIDE A PAIR OF SPRING CONTACT ELEMENTS EXTENDING FROM SAID BODY PORTION, EACH OF SAID ELEMENTS HAVING INNER AND OUTER PARALLEL PLANAR BROAD SURFACES AND TOP AND BOTTOM EDGE SURFACES BETWEEN SAID BROAD SURFACES, SAID ELEMENTS OF EACH PAIR BEING OFFSET LATERALLY OF EACH OTHER TO DISPOSE THE INNER BROAD SURFACE OF EACH ELEMENT IN SUBSTANTIALLY THE SAME PLANE, SAID ELEMENTS OF EACH PAIR BEING POSITIONED WITH PORTIONS OF SAID INNER BROAD SURFACES IN OVERLAPPING RELATION, LEAD MEANS AT THE OUTER ENDS OF SAID ELEMENTS FOR EFFECTING ELECTRICAL ENGAGEMENT OF THE CONTACT ELEMENTS OF EACH PAIR IN AN END TO END DIRECTION, SAID ELEMENTS OF EACH PAIR EXPANDING DURING SAID INTERENGAGEMENT TO CONTACT SAID OTHER PAIR OF ELEMENTS UNDER SPRING TENSION.