US3107961A - Printed circuit edge connector - Google Patents

Description

P. r. HAHN ETAL `PRINTED CIRCUIT EDGE CONNECTOR I Oct. 22, -1963 3 Sheets-Sheet 1 Filed Dec'. 20. 1960 `g\ L Paul NVENTOR. T Hahn and Gilbert C. Sitz y.llllzwhd Illl.

IT EDGE CONNECTOR PRINTED QIRCU Filed D60. v20. 1960 l5 Sheets-Sheet 2 Gibert C. Sat-L f f INVENTOR.

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.0t.22,19 63 P.T.HAHNETA| *3,107,961

' PRINTED cIRcUIT EDGE- CONNECTOR Filed Dec. 2o. 1960 Y l s sheets-sheet s 9e e5 F6 65 '(76 96 :35:: ::7 7a 54 57 6&1 72.

y 9a /6 A gfm/ Oab |02 loo INVENT'oR. Paul T Hohn and Gilbert C. Sitz:-

United States Patent O 3,107,961 PRNTED CiRCUlT EDGE CGNNECTOR Paul T. Hahn and Giihert C. Sitz, Harrisburg, Pn., assignors to AMP Incorporated, Harrisburg, Pa. Filed Dec. 2i), 19e-9, Ser. No. 77,067

9 Claims. (Si. 339-17) p This invention relates to multiple contact connectors for disengageably connecting two groups of conductors with each other. The embodiments of the invention herein disclosed are particularly intended for use with printed circuit boards, however, the principles of the invention are equally applicable to usage with other panellike devices having conductors thereon.

The Widespread adoption of printed circuit Wiring techniques has given rise to the development of connecting devices, commonly called edge connectors, for disengageably connecting the conductors on the board with other conductors which are external to the board. Most of the presently known types of edge connecting devices comprise an insulating block having an opening or trough -therein for reception of a portion of the edge of the board. A plurality of relatively small spring oontacts are mounted in the block and extend into this trough. These contacts are arranged in a manner such that upon insertion of the board, the contacts engage, and establish electrical contact with, the conducting paths on the board. Usually, the contacts are resiliently pressed against the inserted board so that a contact force is established between the contacts and the conducting paths of the board thereby to ensure an electrical connection having a satisfactorily low resistance. A further feature of the presently available edge connectors is that the connector assembly is clamped to the board by the gripping action of the electrical contacts themselves so that these contacts perform both the electrical function of establishing the electrical contact with the conductors and the mechanical function of clamping the connector to the board.

This prior art arrangement is satisfactory under many circumstances but has some inherent disadvantages which can be explained as follows: The board obviously must be clamped by the spring contacts with suiiicient force to hold the parts together and, preferably, this force should be relatively high in order to prevent relative movement between the board and the connector block if either `of these parts is jarred or vibrated. The effect of vibration is particularly important since `if either the block or the board should vibrate, the engagement of the individual contacts with the conductors on the board might be intermittently broken to the detriment of the electrical function of the assembly. However, the contact force which each of the individual contacts exerts upon the conducting paths of the board should not be unduly high since increasing the con-tact force beyond a certain level does not significantly lower the resistance of the contact interface but kdoes substantially increase the wear on the contacts and conductors when the board and block are assembled Ito each other. This wear problem assumes an increased importance if the contacts or conductors are plated, as is common, with gold or tin since, a high contact force will cause the plating to be rapidly worn olf as the contacts slide over the conductors when the board is assembled to `the connector. Thus, with this prior art arrangement, a compromise contact force must be selected which may be unduly high from the wear standpoint but which may be barely adequate and less than optimum from the mechanical standpoint of clamping the board and block together.

The design problem of these prior art type boards is further complicated by the practical diiculty of obtaining this compromise contact force. To illustrate, conventional printed circuit boards usually do not conform to precise thickness tolerances but, because of manufacturing limitations, may vary in thickness Aby as much as 110%. Thus, if the edge connector is manufactured to accept a board having some given nominal thickness, the insertion of a relatively thick board (10% thicker than the nominal thickness) will result in extremely high contact pressures with high attrition of the contact plating upon insertion of lthe board. If the board happens to be relatively thin but still within the tolerance limits, on the other hand, the board Iand. connector will not be clamped together with the requisite degree of rigidi-ty.

It is among the objects of the present invention to obviate some of the foregoing shortcomings of prior art edge connectors.` More specifically, itis an object of the present invention to provide an edge connector or the like in which the means for mechanically securing the board to the panel is independent lof .the contacts in the connector block. A further object is to provide an edge connector which can be assembled to panels of varying thickness without changing the contact force exerted bythe spring contacts in the connector on the conductors on the panel. A still further object is to provide an edge connector forv printed circuit boards which has spring contacts arranged in a manner such that these spring contacts will be resiliently loaded or deflected by the same amount by boards of varying thickness.

These and other objects of the invention are achieved in one preferred embodiment comprising a block having n, a recess or trough for the reception of a portion of the edge of a printed circuit board. One of the longitudinal sidewalls of the trough has barriers or ledges thereon at spaced intervals and the contacts, which are mounted in the block, have iiexible ends which extend into the spaces between these barriers. The contact portions of the contacts (i.e. the surface portions which engage the conductors on the board) are normally disposed outwardly of these barriers with respect to the sidewall of the trough so that upon insertion of the board, these contacts are flexed and the contact portions are moved relatively towards the sidewall until the contact interfaces are in alignment with the barriers. The mechanical clamping of the edge connector to the board is achieved by means of a clamping means which presses the board against the lbarriers described above. With this arrangement, theA clamping force is transmitted through the board and to the barriers so that the contacts could be removed from the connector block and the parts would still be secured together.

The invention is applicable to boards having conductors on only one side thereof and to printed circuit boards having conducting paths on both surfaces. ln the latter case, the dielectric bloc'k is advantageously formed in two sections, each section having a recess so that a trough is defined when the sections are assembled in face-to-face relationship with each other. These two sections are resiliently biased towards each other so that upon insertion of the board, they are in effect, wedged apart by the board against the force of the resilient means. Again, `the sections of the block each have barriers and the contacts are disposed between these barriers. Upon assembly of the connector to the edge of the board, the edge of the board is clamped between the barriers of the Ktwo sections of the block.

In the drawing:

FIGURE l is a frontal view of one embodiment of the invention which is adapted Ifor usage with printed cincuit boards having conductors `on `only one side thereof.

FIGURE 2 is a view similar to FIGURE 1 showing E the positions of the par-ts after insertion of an edge portion of a printed circuit board.

FIGURES 3 and 4 are views taken along the lines and looking in the direction of the arrows 3--3 and 4 4 respectively of FIGURES l and 2.

FIGURE S is a perspective View showing a connector of the type shown in FIGURE l in assembled relationship tothe edge of a printed circuit board.

FIGURE 6 is a frontal view of an alternative embodiment of the invention intended for usage with printed circuit b-oards havin-g conductors on both sides thereof.

FIGURE 7 -is a perspective view of the embodiment of FIGURE 6 and showingV -a printed circuit board in alignment with the ltrough of the block.

FIGURE 7A is ,a fragmentary perspective exploded view of the rear side o-f the embodiment of FIGURE 6.

FIGURE 8 is a fragmentary view similar to FIGURE 6 but showing the positions of the plants after insertion of a printed circuit board.

FIGURE 9 is a view taken along the lines 9 9 of FIGURE 8.

FIGURE l is a vie-w taken along the lines 111.46 of FIGURE 6.

FIGURE l1 is a view showing another embodiment of the invention.

FIGURE l2 is a view similar to FIGURE ll but showing the positions of the parts after insertion of fthe printed circuit board.

The embodiment of the invention shown in FIGURES 1-5 is -intended for usa-ge with the conventional printed circuit board l@ having conductors -12 on one side thereof. As shown in FIGURE 5, these conductors extend to the edge of the board and between notches 11 which are adapted to receive the sides of connector bloicli 2.

The block 2 has a rear surface 4 and .a front surface 6 in which there is a trough-like ope-ning 8 into which the edge of the board is adapted to be inserted. Advantageously, the upper edge and a portion of the side edges of this trough are beveled las shown at 14 to facilitate the insertion of the board. The upper sidewall 17 of the trough, as viewed in FIGURE l, is provided with evenly spaced barriers or ledges 16 having bearing surfaces 18 facing the opposite sidewall 2S of the block and lying in a plane which extends, in the disclosed embodiment, parallel to the plane of the sidewall 17. A plurality of electrical contacts 20 are mounted in the block and yhave end portions 22 extending from the rear surface 4 for attachment to wires (not shown).

The opposite ends 24 extend 4through the surface 19 of the trough and between adjacent barriers. The contact portion of the particular type of contact shown in the drawing has a generally triangular end 26, the apex of which normally is located inwardly (relative to the trough) of the plane defined by the .bearing Vsurfaces 1S. This particular type off contact maybe form-ed from solid stock as by rolling or coin-ing although the principles of the invention are not limited to this form of contact. The important structural relationship of the contacts to, the block is that the -apices of the contact portions are normally disposed inwardly of the plane of the bearing surfaces 18 so that upon insertion of lan edge portion of a board into the trough, the ends 24 of the contacts will be exed only by the amount necessary to move these apices 26 into the plane of the bearing surfaces 8.

The lower portion of the trough-like opening as viewed in FIGURE l is enlarged as shown at 3G and a Igenerally channel-shaped clamping plate 32 is positioned in this portion of the trough. This plate has a flange 34 extending from one of its sides and into an elongated recess or `groove 36 in the surface 19 of the trough 8. The opposite side of the plate has an apron 37 which extends downwardly, -as viewed in FIGURES 1 and 3, towards the side 28 of ythe trough.

A spring 318 is inte-rposed between the underside of pla-te 32 and the side 2S of the trough and normally form of spring may be utilized, the disclosed embodi t ment being an undulating leaf spring having two node-s 40 upon which the underside of the plate rests. The ends of this spring are lodged ybehind ledges 42 which form part of the dielectric block so that after assembly, kthe spring and the apron will be retained in the positions shown in the drawing.

As shown in FIGURE l, fwhen the parts are in their normal positions and before insertion of a printed circuit board, the upper surface of the plate 32 abn-ts the reentrant surf-aces 44 of the trough and is pressed there'- against by the spring 38. Also, the contact tip portions 26 of the contacts are disposed inwardly of the trough with respect to .the plane of these bearing surfaces. Upon insertion of an edge portion of a printed circuit board, the plate 312 is biased downwardly, 'as viewed in FIG- URES l and 2, so that a slight gap 45 (FIGURE 2) exists between the edge portions of the apron andthe rcentrant surfaces 44. The board itself is clamped between the upper surface of the plate 32 and the bearing surfaces 18 of the ledges or barriers while the contacts are flexed as shown in FIGURE 4 until the contact tips or apices 26 are moved into the plane of the bearing surfaces and towards the surface of upper sidewall v17.

,In order to achieve all of the benefits of the inven-v tion, the force exerted by the spring 38 on the printed circuit board should exceed the total force exerted on the board by all of the contacts 23, preferably by -a substantial amount. T0 illustrate lthis point, if it is assumed that ten contacts are provided in a block of the type spring 36 should be of a stiffness such that it will exert Y a force of more than 5 lbs., eg., about l() lbs., on the board after insertion. `If this relationship between the stiffness of the spring and the stiffness of the contacts is maintained, the board 10 will be clamped between sur-L faces 1S and plate 32. If the spring 38 is not sufficiently strong to overcome the stiffness of .the contacts, however, it is possible that the board will not tbe so clamped but will merely be held between the contacts and the plate 32.

The several advantages of the invention can be appreciated from a consideration of the manner in which the printed circuit board is clamped to the block 2 and the manner in which the contacts are flexed or resiliently deformed upon insertion of the board. It will be apparent from FIGURES 2 and 4 that if the contacts werevremoved from the block, the board would still be clamped between plate 32 and the bearing surfaces 18 since the v contacts themselves are not relied upon for the mechani-` cal clamping of the board. Obviously then, the board f can be clamped very firmly, if desired, by merely using an extremely stiff spring 38 and lthis arrangement would be desirable if the connector were intended for usage in an environment where substantial vibration is present.

Alternatively, if the connector is intended for usage under circumstances where substantially no vibration will be encountered and if a low insertion force is preferred, a

relatively weak spring can be employed, however, the spring should be sufficiently stiff to overcome the tacts as explained above.

An added advantage of the arrangement shown is that printed circuit boards are not ordinarily manufactured to extremely close tolerance but will vary in thickness by a substantial extent. The clamping plate and spring in combination with the bearing -surfaces 18 permits connectors in accordance with the invention to adapt themselves Ito any reasonable variation in board thickness so that the use of a connector in accordance with the invention does not require the use of a precisely dimensioned printed circuit board.

An equally important advantage of the invention is COIly that the detiection of the end portions 24 ofthe contacts, and therefore the contact force, is controlled within eX- tremely precise limits. The contacts themselves can generally be assumed to be dimensionally uniform and can be assumed to conform to relatively precise dimensional tolerances. if each Contact is located within the dielectric block with a reasonable degree of precision, the apex 26 thereof will be precisely positioned at a fixed distance from the plane of the bearing surfaces 18, and upon ine sertion of the printed circuit board this contact apex can move only the amount of this distance. The ilenure of the contact portion -24 is therefore precisely controlled and, since this tlexure determines the contact force, the amount of contact force between the contact apex 26 and the path i2 of the printed circuit board is likewise precisely controlled. This lfeature is of considerable importance since the contacts 26 are usually relatively short so that a slight change in the amount by which they are deflected upon insertion of ythe board will result in a fairly substantial change in the amount of contact pressure established. As pointed out above, the contact force should be only sufficiently high to establish a low resistance electrical Contact but should not be unduly high because of the plating wear problem. Obviously then, precise control of this contact force, to achieve the optimum, is an important achievement of the present invention.

An additional desirable feature of the disclosed ernbodiment is that a substantial amount of ilat bearing surface is provided, by virtue of bearing surfaces 18, between the block and the board. The existence of this bearing interface prevents accidental rocking of either of the parts relative to the other; in other words, the board is held between iiat :gripping surfaces 1S, and the surface of plate 32, and is not gripped only by the limited contact surface of the contacts themselves.

FIGURES 6-l0 show an alternative embodiment of the invention intended for usage with printed circuit boards of the type shown at 46 having conducting paths i3 on both of their faces. The embodiment of FIG- URE 6 comprises a pair of dielectric blocks Si), 52 which are substantially similar in construction. In the description which follows, only the block Si? will be described in detail and the corresponding parts of the block 52 will be identied by the same reference numerals as those used in conjunction -with the block 5t? but differentiated by means of prime marks.

Block section Sii has an open sided groove or recess 54 which extends inwardly from two of its adjacent sides so that when this block is placed against its counterpart 52, the two recesses 5d, 54 dene a trough-like opening for reception of an edge portion of the board. The edges S of the block are beveled, as with the previously described embodiment, to facilitate insertion of the printed circuit board. The sidewall S7 of the recess is provided with spaced barriers or ledges 5S similar to the barriers I6, and having coplanar bearing surfaces eil. Contacts d2, which in this instance are formed from sheet metal, are mounted in the block and have wire receiving portions di extending through the rea wall 66. The opposite ends ed of the contacts extend into the recesses 5d and into the spaces between adjacent ledges 6i). The contact portions 7G of the contacts are again disposed out- -\vardly, with respect to the recess sidewall, of the plane delined by the bearing surfaces 6ft. It will be appreciated that the arrangement is substantially similar to the arrangement of parts in the embodiment of `FIGURES 1 5 and that the contact portions 7@ of these contacts are adapted to be moved relatively into the plane of the bearing surfaces upon insertion of the printed circuit board.

An ear 72 is provided on each side of block section S and this ear has a generally cylindrical surface 74 which is adapted to receive the surface of a rivet or the like as described below. A flange 76 extends from the face 7S of the block and functions as a stop or retaining means for a leaf spring 8d. This spring has nodes S2 which normally bear against the top surface 83 of the block. 'Ihe ends `Se of the spring are bent at right angles to the central section thereof and terminate in hooks 86. On one of the ends of each spring, one hook 86 is provided while two hooks are provided on the other end.

The hooked ends 36 of the block 5d are interdigitated with the hooked ends d6 of the block 52 to dene a generally cylindrical surface and a cylindrical pin or rivet `S8 is provided between these hooked ends to hold the parts together. The ends of these pins are hanged as shown at 9d, as by upsetting, so that they will be held in the positions shown in FIGURE 7. The dimensions of the springs are such that the two blocks normally abut each other at their edges 92. The block sections arc, however, capable of relative movement away from each other against the force of the springs Si), 86. Advantageously, the opposed surfaces of the blocks 50, 52 have keying means in the form of a projection 94 and complementary recess so that they cannot be transversely or laterally moved with respect to `each other.

In use, the printed circuit board 46 having the conducting paths d8 on each of its surfaces is inserted into the trough `defined by the recesses 74, 74. The thickness of Ithis board is slightly greater than the distance separating lthe corresponding bearing surfaces 66, 60 of corresponding ones of the barriers 53, 5S so that -upon such insertion, the two blocks are moved relatively apart and the board is clamped between the two sets of ibearing surfaces. The contact portions of the contacts lare, as with the previous embodiment, moved relatively into the planes dened by the bearing surfaces so that again the amount of flexure `imparted to the contacts is controlled within precise limits. It will be apparent that the previously discussed advantages inure to the embodiment `of FIGURES 6-10u The lstiffness of the springs `82 in the embodiment of FIGURE 6 should again be sufficient to overcome the total force exerted by the contacts. If this relationship is maintained, the board will be clamped between the bearing surfaces 60 as shown in FIGURE 8 and will not be held merely by the contacts.

If desired, a block of the type shown alt Sil in FIGURE 6 can be used with 4a single sided panel of the type shown in FIGURES l-6. To achieve this modification (FIG- URE ll), a spring 96 is used having relatively longer end portions 93 than the spring 80 and having reversely bent ends 11%. -A flat panel 102 is interposed between the reversed ends 1% of the spring and the side 104 of the block so that this panel is normally clamped against this side as shown in FIGURE yll. Upon insertion Iof the board, the panel is moved relatively away from the s-urface 164 and the printed circuit board is again clamped between the bearing surfaces of the barriers and the surface of the panel '102.

Changes in construction will occur to rthose skilled in the art and various apparently dilferent'modiiications and embodiments may be made Without departing from the scope of the invention. The matter set forth in the foregoing ydescription and accompanying dnawings is oifered by way of illustration only.

We claim:

l. An electrical connecting device for making disenlgageable electrical connections with electrical conductors on a surface of a panel-like member comprising, an insulating block, a plurality of contact members mounted in said block, said contact members each having a contact portion for engagement with an electrical conductor on said panel-like member said contact portions being disposed outwardly from one surface of said block Ibut being resilienitly movable towards said one surface, said block having a bearing surface ydisposed between said one surface and said contact portions, and clamping means on said block for clamping said panel-like member to said block, said clamping means comprising a clamping surface opposed to, and resiliently biased towards, `said bearing surface whereby, upon insertion of said panel-like member between said clamping surface and said contact portions of said contact members, said panel-like member is clamped against said bearing surface and said contact portions are resiliently flexed and displaced relatively towards said one surface and into the plane of said bearing surface, said contact portions being resiliently biased against said conductors on said surface of said panel-like member as a result of their being iiexed, whereby the mechanical securement of said panel-like member to said block is maintained independently of the electrical contact between said contact portions and said conductors.

2. An electrical connecting device for making disengageable electrical connections with the electrical conductors on a panel-like member comprising, an insulating block, a plurality of contact members in said block, each contact member having a contact portion for engagement with one of said conductors, said contact portions being normally in lalignment with each other lalong a line which is spaced from one ysurface of said block, said contact portions beinrg resiliently movable towards said one surface,V at least one ledge on said one surface, said ledge having a bearing surface which is spaced from said one surface and is disposed between said one surface and said line defined by sai-d contact portions when in their normal positions, and clamping means for holding said panel-like member against said bearing surface, said clamping means comprising a clamping surface opposed to, and r-esiliently biased towards, said bearing surface whereby, upon assembly 'of said panel-like member to said block, said contact portions are resiliently moved relatively towards said surface and resiliently urged against said conductors on said panel-like member, and said panel-like member is clamped against said bearing surface and in assembled relationship to said block by said clamping means, said panel-like member being clamped to said block 4independently of said contact pontions and said conductors.

3. Apparatus as set forth in claim` 2 wherein said block `is provided with a plurality of ledges in spaced apart relationship @and each ledge provides a bearing surface, said bearing surfaces lying in a single plane, and said contacts are disposed in the cavities between adjacent ledges.

4. Apparatus as set forth in claim 2 wherein said block has a trough for reception of said panel-like member, one of the sidewalls of said trough constituting said one surface, and wherein said clamping means is disposed in Said trough.

5. Apparatus as set forth in claim 2 wherein said block comprises two sections, each of said isections having a plurality of contact members therein, the contact members of each seotion being in alignment, each section having a bearing surface for bearing engagement with said panel-like member, and resilient means biasing said blocks towards each other whereby, upon insertion of said panellike member between said sections, said member is clamped between said bearing surfaces and said contacts are resiliently pressed against conducting paths on said member.

6. Apparatus as set forth in claim 2 wherein lsaid block comprises a pair of substantially similar sections, each of said sections having a recess extending inwardly from two adjacent sides thereof, said sections being disposed against each other with said recesses juxtaposed to define a troughlike opening for reception of said panel-like member, each of said sections having a battery of said contact members extending into its respective recess and each having at least one bearing surface in its recess, and resilient means biasing said sections against each other whereby, upon insertion of said panel-like member into said trough-like opening, said panel-like member is clamped between said bearing surfaces and said contact members are resiliently pressed against conducting paths on said panel-like meniber.

7. An electrical connecting device for making disengageable electrical `connections with electrical conductors on a surface of a panel-like member comprising, an insulating block, :a trough in said block for reception of an edge portion of said panel-like member, a plurality of barriers on one of the longitudinal sidewalls of `said trough, electrical contact members in said block having end portions extending into said trough and into the spaces between said barriers, said end portions having contact surface portions for engagement with 'conductors on said panel-like member, said end portions being resiliently movable towards said one sidewall, said barriers being disposed betwen said one longitudinal sidewall and said contact surface portions, and a resiliently biased clamping plate disposed in said trough and facing said barriers,

and spring means normally biasing said plate ltowards said mounted in each of said sections Iand having end portions extending between adjacent barriers, contact portions on said end portions, and said contact portions of each siection being in alignment and bein-g `disposed inwardly of said trough with respect to said barriers whereby, upon insertion of said panel-like member intok said trough, said board is clamped by said resilient means between the barriers of said sidewalls, and said contact portions are resiliently engaged with the conductors on said member.

`9. In combination with la panel-like memlber having electrical conductors on both sides thereof, an electrical connecting device establishing electrical contact with said conductors comprising, an insulating block having a trough, an edge portion of said block extending into said trough, said block being divi-ded into two sections along a plane extending longitudinally through said trough, the

opposed longitudinal sidewalls of said trough having spaced barriers thereon, resilient means biasing said sections towards each other and against `said panel-like member thereby to clamp said block and member together, electrical contact-members mounted in each of said sections and having end portions extending between said barriers, said contacts being resiliently stressed by said panellike member and having contact portions in engagement with said conductors.

References Cited in the file of this patent UNiTED STATES PATENTS 2,731,609 Sobel Ian. 17, 1956 2,857,577 Vanderpool Oct. 21, 1958 2,923,911 Demurjian Feb. 2, 1960 2,965,811 Batcher Dec. 20, 1960 2,968,016 Angelo Jan. 10, 1961 3,003,131 Nystuen Oct. 3, 1961 FOREIGN PATENTS 375,922 Great Britain July 7, 1932

Claims (1)

1. AN ELECTRICAL CONNECTING DEVICE FOR MAKING DISENGAGEABLE ELECTRICAL CONNECTIONS WITH ELECTRICAL CONDUCTORS ON A SURFACE OF A PANEL-LIKE MEMBER COMPRISING, AN INSULATING BLOCK, A PLURALITY OF CONTACT MEMBERS MOUNTED IN SAID BLOCK, SAID CONTACT MEMBERS EACH HAVING A CONTACT PORTION FOR ENGAGEMENT WITH AN ELECTRICAL CONDUCTOR ON SAID PANEL-LIKE MEMBER SAID CONTACT PORTIONS BEING DISPOSED OUTWARDLY FROM ONE SURFACE OF SAID BLOCK BUT BEEING RESILIENTLY MOVABLE TOWARDS SAID ONE SURFACE, SAID BLOCK HAVING A BEARING SURFACE DISPOSED BETWEEN SAID ONE SURFACE AND SAID CONTACT PORTIONS, AND CLAMPING MEANS ON SAID BLOCK FOR CLAMPING SAID PANEL-LIKE MEMBER TO SAID BLOCK, SAID CLAMPING MEANS COMPRISING A CLAMPING SURFACE OPPOSED TO, AND RESILENTLY BIASED TOWARDS, SAID BEARING SURFACE WHEREBY, UPON INSERTION OF SAID PANEL-LIKE MEMBER BETWEEN SAID CLAMPING SURFACE AND SAID CONTACT PORTIONS OF SAID CONTACT MEMBERS, PANEL-LIKE MEMBER

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