US3094364A

US3094364A - Connector mounting

Info

Publication number: US3094364A
Application number: US41560A
Authority: US
Inventors: Thomas R Liagg
Original assignee: AMP Inc
Current assignee: TE Connectivity Corp
Priority date: 1960-07-08
Filing date: 1960-07-08
Publication date: 1963-06-18
Anticipated expiration: 1980-06-18
Also published as: GB918009A; CH396129A; NL266688A; DE1515362A1

Description

June 18, 1963 T. R. LINGG CONNECTOR MOUNTING 2 Sheets-Sheet 1 Filed July 8. 1960 INVENTORS, THOMAS R. UNGG June 18, 1963 1'. R. LINGG 3,094,364

CONNECTOR MOUNTING Filed July 8. 1960 2 Sheets-Sheet 2 INVENTOR. THOMAS R. UNGG M,Wr W

United States Patent 3,094,364 CONNECTOR MOUNTING Thomas R. Lingg, Camp Hill, Pa., assignor to AM Incorporated, Harrisburg, Pa. Filed July 8, 1960, Ser. No. 41,569 4 Claims. (Cl. 339-64) This invention relates to electrical connectors and particularly to a connector having an improved mounting means for mounting the connector assembly in a panel or the like.

The term electrical connector can be interpreted in a generic sense to connote virtually any type of device for connecting the end of a wire to a similar device or another mating part. In a narrower sense, however, the term electrical connector is often employed with specific reference to a device comprising a dielectric body, such as a cylindrical or rectangular body, having a number of openings therethrough in which there are mounted contacts, such as contact pins or contact sockets. An electrical connector of this type is engageable with, and disengageable from, a complementary connector to form a disengageable electrical and mechanical connection between a large number of wires. The present invention is related to electrical connectors of this type.

In accordance with one known technique for mounting electrical connectors, a first connector is inserted through an opening in a first panel and clamped or secured thereto. The second connector is similarly secured to a second panel so that when the panels are moved relatively towards each other with the two connector parts or halves in axial alignment, the contacts in the connectors will be engaged with each other. The first panel may constitute one side of an enclosure or box and the second panel in which the second electrical connector is mounted may constitute a cover for the box so that when the cover is assembled to the box the two connector parts will be engaged with each other. Since the two electrical connector parts must be in axial alignment with each other, it follows that the two panels must be substantially parallel to each other and the open ings in the panels in which the connectors are mounted must be in axial alignment with each other. The contacts within the connectors are relatively small and may have a diameter of about 0.030 or less and a great number of contacts are frequently provided in a single connector assembly, for example, connectors having as high as 100 contacts therein are not uncommon. It will be appreciated then that if the connectors are rigidly mounted in the panels and the panels are adapted to be secured in spaced apart relation by some rigid clamping or securing means such as screws, the entire assembly must be manufactured to a very high degree of dimensional precision. For example, the openings in the panels in which the connectors are fitted must be provided on very carefully positioned centers and the clamping or securing means for holding the panels in spaced relationship to each other must also be precisely positioned and must be manufactured to close dimensional tolerances to assure axial alignment of the connectors. The manufacturing techniques required to provide such close dimensional control are always more expensive than would be the case if a wider range of tolerances were permitted. It would be desirable then to provide a mounting means for the connectors in the panels which would not impose unreasonably precise manufacturing requirements and which would permit the connectors to be assembled to the panels in a minimum time but which at the same time would insure accurate and precise mating of the connectors in the two panels.

It is accordingly an object of the present invention to provide an improved electrical connector having means for mounting the connector on a panel or the like. A

ice

further object is to provide an electrical connector having a mounting means thereon which permits limited movement of the connector body to permit the connector to align itself with a mating connector upon movement of the two connector parts into engagement with each other. A more specific object is to provide a mounting means for a connector assembly which permits both lateral and oblique reorientation of the connector body upon its being engaged with a complementary connector body. A still further object of the invention is to provide a connector assembly having a self-contained means for resiliently urging the contacts of the connector into the mating contacts of a complementary connector which means does not rely upon the spacing of the panels in which the connector assemblies are mounted.

These and other objects of the invention are achieved in a preferred embodiment comprising a connector body having a radially extending collar intermediate its ends. A cylindrical guide member is concentrically arranged around the connector body and extends beyond the one end thereof in which the ends of the contacts within the connector are disposed. This guide member has an inwardly turned flange at its end which abuts the collar mentioned above so that the guide cannot move off of the connector body and past the one end of the connector body. A housing is provided in surrounding relationship to the connector body and also in surrounding and partially overlapping relationship with the guide member. An inwardly turned flange on this housing engages a radially extending flange on the guide member so that the housing cannot move axially of the connector body towards the end which is opposite to the one end on which the guide is provided. The housing has an inwardly oifset portion which defines a shoulder in opposition to the previously mentioned flange on the guide and a spring is interposed between this shoulder and the collar on the guide to urge the guide member against the flange of the housing. This arrangement permits relative movement of the guide member towards the other end of the connector and towards the reduced diameter portion of the housing. The reduced diameter portion of the housing which is formed by the inwardly offset end is adapted to be inserted into an opening in a panel and a clamping means such as a threaded nut on the end of the connector body, clamps the connector to the panel. The arrangement is such that the connector body and the guide can be displaced laterally of their normal axis and can also be displaced obliquely of this axis so that if a mating complementary connector is moved into engagement with a connector having the above-described panel mounting, the connector body can realign itself relative to the panel until it is in axial alignment with the complementary connector.

In the drawings:

FIGURE 1 is a perspective view of one form of panel mounting means for electrical connectors illustrating one environment in which the invention is used;

FIGURE 2 is a side view partially in section showing a connector assembly in accordance with the invention mounted in a panel and also showing a complementary connector in a panel parallel thereto;

FIGURES 3, 4 and 5 are views similar to FIGURE 2 but illustrating the manner in which a connector panel mounted in accordance with the invention will realign itself in the event of initial non-alignment with the complementary connector in the mating panel;

FIGURE 6 is a view taken along the lines 6-6 of FIGURE 2;

FIGURE 7 is a view illustrating axial displacement of a connector mounted in accordance with the invention; and

FIGURE 8 is a side view of an alternative embodiment.

will not extend obliquely of each other. the holes in the web 7 and the cover plate 12, in which The precise nature of the problem to which the instant invention is addressed can best be explained with reference to FIGURE 1 wherein the reference numerals 2 denote connectorassemblies mounted in accordance With the invention in the web portion 7 of a channel-shaped bracket having legs 6 which are secured, as by welding, to the back wall of a housing or box 8. This box has inwardly turned flanges on the open face thereof to provide a bearing surface for a cover plate 12, a clamping means in the form of threaded

openings

14, 16 through which screws are adapted to be inserted, being provided in the cover plate and flanges 1.0 to secure the cover plate in place. The complementary connectors 4 are rigidly mounted in openings in the cover plate so that when the plate is secured in place as by fasteners, the complementary connectors 4 will be mated with the connectors 2 on the web 7 of the bracket. Each conhector in the disclosed form of the invention contains a dielectric insert 18, in which a plurality of openings w are provided for the contacts. The connector part 4 contains socket-type contacts (which are not visible) for the reception of pins in the connector 2. As is evident from the drawing, these contacts are very closely spaced togetherand are relatively small so that the two connector '

parts

2, 4 must be in substantial axial alignment when they are engaged with each other in order to avoid damage to the contacts and to achieve proper electrical contact of the parts.

If the connector assemblies 2 are rigidly secured to the web 7 and the connector assemblies 4 are rigidly secured to the cover plate 12, it will be apparent that the entire assembly shovm in FIGURE 1 must be made with a great deal of precision. Thus, the flanges 16 of the box 8 must all -be substantially parallel to the surface of the web 7 so that the axes of the connector parts 2, 4 F uithermore,

the connectors are mounted, must be very precisely located on the same axis and the threaded Openings 14,

16 must also be precisely located so that the

connector parts

2, 4 will, in fact, be in axial alignment. Obviously, the imposition of such high manufacturing standards would greatly increase the cost of the assembly shown in FIGURE 1, and furthermore the mass production of such assemblies with interchangeable parts would not be practical. The essential purpose of the instant invention then is to provide a mounting means for the connector 2 which will assure proper mating of the complementary connectors 4 with the connectors 2 even if, for example, the flanges 10 are not parallel to the plane of the web 7, or if the openings in the web or the cover plate 12 are .not perfectly located. The manner in which this objective is achieved will be apparentfrom the description of the preferred embodiment which follows.

Referring now to FIGURE 2, the disclosed embodiment of the invention comprises a connector body which includes a cylindrical metal-lie shell 22, in which the dielectric insert 18 is mounted. As shown in FIGURE 6, a

. key 21 .in' the shell permits insertion of the insert only end of the shell=-to protect the contact pins 20. The connector body portion 22 is adapted to receive the end 28 of theconnector part4 which has :a radial flange 32 by means-of which it is secured to the panel 12. Advantageously, radially extending pins 30 are provided at spaced intervals around the circumference of the reduced diameter end of connector part 4 to assist in centering it as will be apparent from the description below. In the disclosed embodiment it will be noted that the righthand end of the connector part 4 is threaded as shown at 34.

-Quitefrequently, the ends of these shells are threaded as shown to permit the parts to be coupled to a cable clamp or to adapt them to be otherwise assembled to other connectors. It will be understood that the insert 18 within shell 28 is keyed in the same manner as the insert in shell 22, e.g. by means of :a key and slot similar to that shown at 21.

As shown in FIGURES 24, the external surface of extension 26 is provided with keys 29, the sides of which taper towards each other at their ends 31. Additionally, the surfaces of these keys at their ends are inclined towards the shell axis. These keys are received within complementary keyways (not shown) on the internal surface of shell member 28, the tapered ends of the keys being provided for the purpose of guiding the two connector parts into engagement with each other in the event of initial non-alignment.

A cylindrical guide member 36 surrounds the end of shell 22 and has on its left-hand end an inwardly turned flange 38 which normally abuts collar 24 to prevent rightward movement of the guide 36 from the position shown in the drawing. Advantageously, the edge of this-inwardly directed flange 38 bears against the cylindrical surface of the portion 22 of the shell so that it is not capable of substantial lateral or oblique movement relative to the shell; in other words, the inwardy turned flange should lit the cylindrical surface 22 with sufficient closeness so that the hood member or guide 36 will be maintained in substantial axial alignment with the shell member and with the extension 26 thereof. In the embodiment shown, the guide is not secured to the shell although it may be so secured, or integral with the shell if desired.

Intermediate its ends there is provided on the guide member a radially outwardly extending collar or flange 42 which abuts a radially inwardly directed flange 46 of a cylindrical housing 44 which is in surrounding and overlapping relationship to the guide 36. Flange 42 of the guide 36 is slightly shorter than inwardly directed flange 46 on housing 44 so that the shell 22 and the guide can be later-ally or obliquely moved from the position shown in FIGURE 2 and out of exact concentricity with housing 44. This feature is of importance to the utility of the device as will be apparent from the description below. The left-hand end'of the housing 44, as viewed in FIG- URE 2, is radially inwardly offset to define a shoulder 4-8 which is opposed to, and spaced from, the face of flange 42 and a compressed helical spring 50 is interposed between this flange and the shoulder 48. This spring normally biases the flange 42 against the inwardly directed flange 46 of the housing so that the parts are substantially in their normal positions in FIGURE 2.

The reduced diameter end 52 of the housing extends into the opening in the panel 7 and the entire assembly is clamped in place by means of :a nut 54threaded onto the left-hand end of the shell 22. This reduced diameter portion should have a relatively snug fit within the opening although the opening will ordinarily be slightly oversized relative to the end of the housing to permit facile assembly of the connector to the panel.

It will be apparent that the

connectors

2, 4 must be mounted in the

panels

7, 12 in proper rotational alignment with each other. As shown in FIGURE 6, such rotstional alignment is achieved by means of a key 56 in the connector shell 22 which extends through a slot in housing 44 and through a notch 58 in the panel opening. The notch 58 is slightly oversized to permit swiveling of the housing relative to the panel as described below. A similar key arrangement is provided for the connector part 4 although the notch is not oversized since this part is rigidly mounted.

Under ideal conditions of use, the parts will be in substantially perfect alignment as shown in FIGURE 2, and under these circumstances when the plate 12 is moved relatively towards the plate 7 (as when the cover plate is fastened onto the box in FIGURE 1) the connector part 4 will move axially over the extension 26 of the connector part 2. As explained above, however, the ideal and perfeet conditions are not always obtained, and if dimensional perfection is not achieved the situation shown in FIGURE 3 may exist; that is, the plane of panel 12 may extend obliquely of the plane of panel 7 rather than parallel thereto. Under these circumstances, the axes, denoted by the letters A-A and BB, of the connectors will not be in alignment with each other but will extend obliquely of each other. The condition shown in FIGURE 3 will arise, for example, if one of the legs of the bracket 6 is shorter than the other of the legs, or if the back of the box 8 is not substantially parallel to the four inwardly directed flanges 10 on the front thereof.

When the parts are misaligned as shown in FIGURE 3, the connector assembly 2 will realign itself during the movement of the connector part 4 thereinto as shown in FIGURES 4 and 5. In FIGURE 4 it will be noted that the reduced diameter end of the shell has entered the flared-out mouth of the guide 36 and the radially extending pins 30 are beginning to contact the inside surface of the guide. Upon further leftward movement of the panel 12 and connector part 4, this connector part will push the guide member 36 upwardly and, since the guide member itself is not laterally movable with respect to the shell 22 because of the relatively close fit of the flange 38 on the surface of the shell, the shell itself will also be cocked upwardly as shown in FIGURE until the axes A-A, B-B are brought into coincidence. It will be noted at FIG- URE 5 that the upper portion of the helical spring as viewed in this figure is further compressed during movement of the plate 12 towards the plate 7 and that such compression of the spring is necessary in order to achieve the axial alignment of the connector parts.

In some instances it will be necessary to rotationally align the housing 22 relative to the connector part 4 since the key 56 and notch 58 do not fit together tightly. If such realignment is necessary, it is achieved by virtue of the tapered and inwardly inclined ends of the keys 29 which enter the complementary slots of the shell 28 and, if necessary, cause the shell 22 to be slightly rotated by ca-mming action to bring it into proper alignment.

The invention has beneficial effects in situations other than the precise situation shown in FIGURES 3-5. For example, the panels 7-12 might be in perfect parallelism with each other, but the openings in the panels may be offset somewhat due to imperfect manufacturing techniques. Under such circumstances, the axes AA, B-B would be parallel to, but offset from, each other. Under such circumstances, a connector in accordance with the invention would again permit lateral movement of the connector body 22 relative to its housing in order that it might align itself with the complementary connector body 4.

FIGURE 7 shows still another situation in which the practice of the invention will achieve substantially perfect mating of two connector parts in spite of imperfections in the panels. In this figure, it is assumed that the two

panels

7, 12 are provided with clamping means to secure them in spaced-apart relationship, indicated by the letter C. For example, the clamping means for the panels can be visualized as the flanges and the screws which extend through the

openings

14, 16 of FIGURE 1. It is assumed in FIGURE 7, however, that the clamping means are imperfect in that the spacing C is less than the spacing which would cause the two connector parts to be properly mated. It will be apparent upon reflection that if the connectors were rigidly mounted in their panels, this improper spacing of the panels would prevent clamping of the panels together, i.e. in FIGURE 1, the cover 12 could not be clamped against the flanges 10 because the connector parts would become fully engaged before the cover would be fully seated on the panels. Where the connector assembly 2 is mounted in accordance with the invention, however, the panels can be clamped as shown since the connector body 22 will axially retract against the force of spring 50, as shown in FIGURE 8. Advantageously, this spring should exert a force against flange 42. which is at least equal to the force required to engage the connectors with each other so that the two con- 6 nector parts will be urged into complete engagement under the conditions of FIGURE 7.

In the drawing the connector part 2 is shown as be ing assembled to a panel. Ordinarily the user of the connector will assemble it to the panel himself and the connector part itself will be supplied by the manufacturer with the guide and housing in place and with these parts retained on the connector shell by means of the nut 54. When the user then wishes to assemble this part of the connector to a panel, he need merely remove the nut 54, insert the connector through the opening in the panel as shown in FIGURE 2, and thread the nut onto the end of the connector to clamp it in place. It is one of the advantages of the invention that the mounting means which permits movement of the connector shell after it has been mounted in the panel is self-contained on the connector shell, and it is unnecessary to work with any additional parts beyond those which were previously used with the prior art type connectors when mounting the connector in a panel.

FIGURE 8 shows an alternative embodiment of the invention in which the housing 44' constitutes a simple spring seat for a volute spring 50'. This spring seat functions to maintain the spring in substantially concentric alignment with the panel opening and is clamped to the panel in the same manner as the housing 44 of FIG- URE 2. It will also be noted that the spring in FIG- URE 8 bears against the outwardly turned end of the guide member rather than an intermediate flange as in FIGURE 2.

The embodiment of FIGURE 8 serves the same purpose as the embodiment of FIGURE 2 in that it permits axial, lateral, and swiveling motion of the connector body relative to the panel. A comparative advantage of the embodiment of FIGURE 12 over that of FIGURE 8 is that in FIGURE 2, the spring is maintained in its compressed condition by the housing and particularly by the arrangement of the

flanges

42, 46. Thus with this embodiment, the spring can be compressed when the connector parts are assembled by the manufacturer and the person who mounts the assembly on the panel 7 need not compress the spring at the time of mounting. With the embodiment of FIGURE 8, however, the spring must be compressed at the time the assembly is mounted on the panel. If desired, this shortcoming of the FIGURE 8 embodiment can be overcome by compressing the spring 50' when the parts are assembled by the manufacturer and the spring can be held in the compressed condition by wrapping wire around the coils. This wrapping would then be removed after the assembly had been mounted on the panel to permit the spring to perform its intended function.

The invention has been herein explained and illustrated in only one environment, the relatively simple arrangement of FIGURE 1. The utility of the invention is not limited to this arrangement but extends to many other connect-or mounting arrangements where the connector parts are secured to panels. Furthermore, it should be noted that the principles of the invention are applicable to non-circular connectors of the type commonly used.

Changes in construction will occur to those skilled in the art and various apparently different modifications and embodiments may be made without departing from the scope of the invention. The matter set forth in the foregoing description and accompanying drawing is offered by way of illustration only. The actual scope of the invention is intended to be defined in the following claims when viewed in their proper perspective against the prior art.

I claim:

1. A connector assembly adapted to be inserted through an opening in, and secured to, a panel, said assembly comprising, a connector body having contact means therein terminating adjacent one end thereof, a guide member mounted on, and in coaxial surrounding relationship with, said body and normally extending beyond said one end, a housing-in surrounding relationship to both said connector body and said guide member, opposed shoulder means on said housing and said guide member for preventing movement of said housing towards the opposite end of said connector body, removable enlarged means on said connector body at the end thereof opposite to said one end, shoulder means on said housingopposed to said enlarged means thereby to permit clamping of said assembly to a panel between said enlarged means and said shoulder means, and compressed resilient means acting between said housing and said guide member and bearing said housing towards said opposite end, said resilient means exerting a force on said guide member and housing which is substantially equal to the force required to engage said connector body with a complementary connector body whereby, upon securing said housingto said panel, said connector body is centrally supported in said panel opening, and upon relative movement of a mating connector body into said guide member, said connector body will align itself with said mating connector body in the event of initial nonalignment and will move axially away from said other connector body in the event of improper spacing of said panels.

2. A connector assembly adapted to be inserted through an opening in, and secured to, a panel, said assembly comprising, a cylindrical connector body having contact means thereon terminating adjacent one end thereof, a circumferential collar integral with said connector body intermediate the ends thereof, a cylindrical guide in surrounding concentric relationship with said body and normally extending beyond said one end, said guide having an inwardly directed flange defining a shoulder in opposed relationship to said collar to prevent movement of said guide in a first direction beyond said one end, a cylindrical housing in surrounding relationship to said connector body intermediate the ends thereof and in surrounding and overlapping relationship with said guide, a radially inwardly directed flange on said housing and a radially outwardly directed flange on said guide, said flanges being in abutting relationship to prevent axial movement of said housing towards the opposite end of said connector body, said housing having a radially inwardly offset portion adjacent the end thereof which is remote from said first end of said connector body, said radially inwardly offset portion defining a shoulder which is opposed to said outwardly directed flange on said guide, a compressed helical spring in surrounding relationship to said connector body and interposed between said shoulder and said outwardly directed flange, said spring exerting an axial force on said guide member and connector body which is substantially equal to the force required to engage said connector body with a complementary connector body, and said spring functioning normally to support said connector body substantially centrally in said housing, a nut on the end of said connector body opposite to said one end thereby to perrnit clamping of said assembly to said panel with said panel contained between said nut and said radially inwardly offset portion of said housing, whereby upon clamping said housing to said panel, said connector body is normally substantially centrally supported in said opening but is capable of movement for alignment purposes upon assembly of a complementary connector body thereto.

3. A connector assembly adapted to be inserted through an opening in, and secured to, a panel, said assembly comprising, a cylindrical connector body having contact rneans thereon terminating adjacent one-end thereof, a circumferential collar integral with said conguide having an inwardly directed flange defining a shoulder in opposed relationship to said collar to prevent movement of said guide in a first direction beyond said one end, theedge of said inwardly directed flange having a relatively close fit around said connector body to prevent lateral movement of said guide relative to said body, a cylindrical housing in surrounding relationship to said connector body intermediate the ends thereof and in surrounding and overlapping relationship with said guide, a radially inwardly directed flange on said housing and a radially outwardly directed flange on said guide, said flanges being in abutting relationship to prevent axial movement of said housing towards the other end of said connector body, said flange on said housing being radially longer than said flange on said guide thereby to permit swiveling movement of said guide and said connector body, said housing having a radially inwardly offset portion adjacent said other end of said connector body defining a shoulder which is opposed to said outwardly directed flange on said guide, a compressed helical spring in surrounding relationship to said connector body and interposed between said shoulder and said outwardly directed flange, said spring exerting an axial force on said guide member and connector body which is substantially equal to the force required to engage said connector body with a complementary connector body, said radially inwardly oflFset portion defining a reduced diameter end portion on said housing for insertion into said opening, and removable enlarged means on said connector body for clamping said housing to said panel with said panel extending between said shoulder and said removable means, whereby, upon clamping said assembly to said panel, said connector body is normally substantially centrally supported in said opening but is capable of movement upon assembly of a second connector body thereto.

4. Electrical connecting means comprising a panel, a connector body extending through an opening in said panel which is oversized relative to said connector body, one end of said connector body being on one side of said panel and the other end of said body being on the opposite side of said panel, a guide member in coaxial surrounding relationship with, and mounted on, said connector body on said one side of said panel and normally extending beyond said one end, a cylindrical housing on said one side of said panel in surrounding relationship to said connector body and in surrounding and overlapping relationship with portions of said guide member, opposed abutting shoulders on said housing and said guide, the end of said housing adjacent said panel being inwardly offset to define a second shoulder in said housing, a coil spring acting between said second shoulder and said guide, the inwardly'offset portion of said housing being received Within said oversized opening in said panel, and means on said other end of said connector body to prevent passage thereof through said opening, said abutting shoulders of said guide member and said housing permitting limited movement of said guide thereby to effect limited movement of said connector body for alignment purposes upon relative movement of a mating panel mounted connector body into said guide.

References Cited in the file of this patent UNITED STATES PATENTS 2,212,728 Blood Aug. 27, 1940 2,377,872 Farrington et al June 12, 1945 2,505,163 Wanner Apr. 25, 1950 2,735,965 Balanda Feb. 21, 1956 2,939,102 Johnson May 31, 1960 FOREIGN PATENTS 807,744 Great Britain Jan. 21, 1959

Claims

4. ELECTRICAL CONNECTING MEANS COMPRISING A PANEL, A CONNECTOR BODY EXTENDING THROUGH AN OPENING IN SAID PANEL WHICH IS OVERSIZED RELATIVE TO SAID CONNECTOR BODY, ONE END OF SAID CONNECTOR BODY BEING ON ONE SIDE OF SAID PANEL AND THE OTHER END OF SAID BODY BEING ON THE OPPOSITE SIDE OF SAID PANEL, A GUIDE MEMBER IN COAXIAL SURROUNDING RELATIONSHIP WITH, AND MOUNTED ON, SAID CONNECTOR BODY ON SAID ONE SIDE OF SAID PANEL AND NORMALLY EXTENDING BEYOND SAID ONE END, A CYLINDRICAL HOUSING ON SAID ONE SIDE OF SAID PANEL IN SURROUNDING RELATIONSHIP TO SAID CONNECTOR BODY AND IN SURROUNDING AND OVERLAPPING RELATIONSHIP WITH PORTIONS OF SAID GUIDE MEMBER, OPPOSED ABUTTING SHOULDERS ON SAID HOUSING AND SAID GUIDE, THE END OF SAID HOUSING ADJACENT SAID PANEL BEING INWARDLY OFFSET TO DEFINE A SECOND SHOULDER IN SAID HOUSING, A COIL SPRING ACTING BETWEEN SAID SECOND SHOULDER AND SAID GUIDE, THE INWARDLY OFFSET PORTION OF SAID HOUS-