US2420880A - Snap switch - Google Patents

Description

May 20, 1947- R. HETHERINGTON 2,429,880

SNAP `SWlTCI-I Filed April l2, 1944 5 Sheets-Sheet l May 20, 1947. R. HETHERINGTON SNAP swITcH Filed April vL?. 1944 5 Sheets-Sheet 2 May 20, 1947.

R. HETHERINGTON U slm swITcH .Filed April 12. 1944 *5 Sheets-Sheet 3' f1/sas...

Patented May 2120,. i947 UNITED STATES PATENT OFFICE SNAP SWITCH Robert Hetherington, Sharon Hill, Pa., assigner to Robert Hetherlngton & Son, Inc., Wilming ton, Del., a corporation of Delaware :n Application April 12, 1944, Serial No. 530,625

14 Claims. (Cl. ZOO-159) 2 My invention relates to electric snap switches 2 and 3 in the relation in which they occur but of a type in which a snap disc carries contact spaced from each other, prior to assemblage. arms at its edges. turned transversely with re- Figure 4"- is a. fragmentary view similar to Figspect to the disc and thrown by ilexing a iorwardure 4, showing another form. ly convex dise through its center plane to rear- 5 Figure 5 is a perspective View of an insulationwardly flexed position and retracting it byaspring enclosed part of the structure in Figure 2, parcompressed in the throwing operation. tially assembled, before it has been fully assem- A purpose is to provide a bridge across interior bled within the outer case.

switch casing insulation, which bridge may limit Figure 6 is a perspective View of a second form the extent of stroke of the disc and support a re- 10 of the invention.

tracting compression spring. Figure 7 is a longitudinal section of the struc- A further purpose is to support a switch snap ture of Figure 6 upon an enlarged scale showing disc upon an insulation bridge transverse to the a different Way in Which the dSC iS grounded t0 switch body. the casing.

A further purpose of the invention is to ground Figure 7 iS a fragmentary seGtOrl 0f the structhe disc so that two outside grounded circuits can ture of Fig. 'l but adapted to normally closed cirbe closed at the same time and opened at the same cuits. time. Figure 8 is a section taken upon line -B in A further purpose is to use a snap switch disc as Figure '7.

the basis for grounding circuits connected with Figure 9 iS a Section taken upon line 9-9 in the disc. Figure 7.

A further purpose is to enclose the switch with- Y Figure 10 iS a Perspective View 0f the disc and in a metallic casing and ground the disc through arms Showing the general type of snap element a flnger extending against the lateral interior of used With Some Slight Variations in Figures 1, 2,

the casing. 3, 4, 5, 6, '7, 8, 9, 10, 11, 12, 13, 14 and 15.

A further purpose is to ground the dir"- through AFigure 11 iS a perspective View of a slightly difa metallic casing, metallic pressed button and a ferent form. spring, Figure 12 is a central longitudinal section to A further purpose is to apply .the same type of enlarged scale of the structure seen in Figure 11.

grounded circuit disc snap switch to either nor- Figure 12 is a fragmentary Section 0f the Strucma'ily open or normally closed circuit use. ture of Figure 12 but adapted to normally closed A further purpose is to'form a compact, sturdy, circuits. spring retracted snap switch of general disc type. Figure 13 iS' a fragmentary lOIlgiiudnal Section Further purposes will appear in the speciilca- Corresponding t0 the lower parts of Figures 12 tion and 1n um claims, 35 and 12B, but taken at right angles to the planes I have preferred to illustrate my invention by 0f the Sections in these tWO figures. a few forms only, selecting forms which are prac- Figure 14 is a Section 0f Figure 12 taken 1111011 tical, eicctive, reliable and inexpensive but which line "-44- have been selected primarily because they well Figure 15 is a top Plan View 0f an insulation illustrate the principles involved. unit Seen in Figure 12.

Figure 1 i5 a, perspective view t0 reduced Scale I In the drawings similar numerals indicate like of a structure embodying one form of my inven- Partstion. The switches shown are all snap switches of Figure 2 is a longitudinal section through the 'the WD@ in Which a snap disc is normally 60nlength oi the switch of Figure 1, as applied to a 45 vexed flwardly either by its own normal snap normally open circuit position or by a retractive spring which is com- Figure 2 is a fragmentary central, longitudipressed against the rear of the disc and throws nal section of a form of the invention applied to the disc forwardly. The disc carries contact 4 normally closed circuits. arms, preferable with contact pads at the ends Figure 2b is a fragmentary section similar to 50 v0f the arms, by which arms (with or without the Figure 2, but showing another form. pads) the actual contacts are made and opened. Figure 3 1s a section on the lines 3--3 of Figure In all of the illustrations, outside connections 2H. are made through binding posts at the rear, sup- Figure 4 is a perspective view showing the variported in insulation and connected with or disout elements involved in the switch of Figures 1, connected from contact stripslic casing in any suitable way, such as by mount,-`

ing the switch upon a grounded board or other support.

In each of the groups of Figures 1-5 and 2,

6-10, and 7"; and 11-15 and 12a, generally similar switches are shown as connected to operate as normally open switches in which the arms are separated from contacts outside of the arms and are closed by movement of the switch as in Figures 2, 7 and 12, or as normally closed switches as seen in Figures 2a, 7a, and 12a.` Comparison of these illustrations 2 and 2H; 7 and 7a, 12 with 12i shows how easily adaptable the presentv invention is to normally open or normally closed switches..

Taking up rst `the description of the form shown in Figures 1-5 and 2a: The'outer casing 20 is threaded at 2| for mounting upon a switch boardor other support. vVIS/here the outside circuits are to be grounded through a disc this casing will be of electrically conducting material which in this art means normally metallic material.

The grounding through its switchboard or other mounting, permissible in all of the forms shown, and intended where two grounded circuits are concurrently to be closed and opened, isshown diagrammatically at 22.

The interior of the casing is insulated to prevent improper grounding or contact o parts of the circuit or circuits. Various types of insulation are shown in Figures 2, 7 and l2 but they have in common insulation of the switch parts and bridge support of the snap disc by which the contacts are made and broken. v

The binding postsalso variously constructed in the different figures, are shown at2v3, k24 in Figure 2 within block insulation 25 and .terminating rearwardly in nuts 26 and washers 21 by which outside conductors 28 and 23 are held irrplace against washers 39." The binding posts support interior fixed contact ,stripsk 3| and 32. It will be noted that these contact strips could be supportedat 33 or not supported by the insulation and are here not supported against interior insulation, so that if desired, this form of unsupported stripcan be used to provide additional spring for the contact, cooperating with the spring of the disc arms to give resilience ,to Ithe contacts made. With the contact strips (3l' only, shown) in Figure 2a the strips may or may not be supported against the insulation at 34 according to whether rigidity or resilience be sought. Spring is provided in Figure 2a by omitting this support.

. The ycontact; strips are protectedagainst. engagement with the metallic casing by an interior sleeve-like part35 of an insulation block 36 (Figure 5) and at the front in Figure 4a the insulation issupplemented by cover 31 apertured at 38 to permit plunger access to ,disc` 39. a

The disc is held in place beneath the cap or `cover and against the ends of yan insulation bridge 40 so as to seat the outer part olfthe disc at the ends of this bridge to hold the disc accurately in position. a a e Thesleeve and disc may be held in` position within the metallic l'casing by'ltheir4 friction t merely as is preferably thecase'or additional means of holdingtliemin-y placlernay.v beused as shown by the screws 4| for the rear block in Figure 1. The cap and cover are pressed against a shoulder 42 so that a friction fit of the cap, the sleeve and the rear block insulation may become effective to maintain all these parts tightly in position.

The cap preferably does not engage directly with the disctohold the disc in position against the bridge as a little play is desirable.`

There are Various ways in which the disc may s be grounded to the casing. Two only are shown,

both of them preferably connecting laterally at the cap. One is shown in the structure of Figure 4 and the other is shown in the fragmentary view Figure 4a. y

n the Figure 4 yform the cap 3l is electrically conducting and makes good contact with the casing, permissibly being inserted tightly as by making it a drive fit. In this form the cap 3l is electrically connected with the disc through a ring 43 which is dished (forwardly concave in 4 radial sections) on the side toward the cap. The ring must be electrically conducting also and yields so as relatively to ilatten under pressure .I and spring outwardly as released. Itsforwardly facing edges 432,` 433 rest against and spread against the rearward `faceof the transverse flange of the cap, whije the rearwardly convex central part of the ring electrically and mechanically engages with the outer edges of the disc.

In `the form shown in Figure 4 the cap 31. is-or may be-insulating. Assuming that the cap is of insulating material, itis notched at 45 to permit the extension of a` tang 44 rearwardly from an outer part of the ring into spring contact; `with-the casing. Since there is no'object in attempting to get ygood contact vbetween the 4discI and the cap the ring 43', still electrically conducting, may be fiat and firmer or more solid thanwould desirably be the case where-the ring is intended to be sprung to give follow-up effect between the cap and the disc.

In 'either event, whether` the form be that of Figure 4j or of Figure '4*1, grounding takes place vthrough the disc, the' ring and the casing. r

All of the constructions shown in the figures lcan be grounded in the same ways as in Figures 2, 2"-,`4 and 4'.

Referring to Figures 2 and 2a, the bridge ln these twoflgures (seen also in the lower part of Figure 4) is forwardly concaved at 46 so as to give support at its diametral ends 41 to the disc at a levelr farther forward than the level 48 at thevsectioned position in Figures 2 and 2.

Initially the'disc is convexed forwardly at 39' in front of the bridge. It may be pressed toward' this position, (normally retracted to this position) 4by a spring 49 seated in recess 50 within the bridge.

lcally conductingpads 56, 51) make the actual contact with the strips (whetheroutside or inside the'armsyin the closed switch position. v

As previously suggested,`the free position of the strips inFigure l3, spaced 'from' the interior of the insulation, permits the strips to take up part 4of the springlof' contactfvso'ias to ensurefa more yielding contact than would otherwise take place and giving slight wiping movement to the contact engagement.

The position of the parts seen in Figure 2 is the normal position of the parts for the normal open circuit switch shown in this gure. 'Ihe disc is convexed forwardly and the lower ends of the arms are turned inwardly toward each other. The convexity of the disc, forwardly Vin theposition of Figure 2 and rearwardly when the contact is made, is controlled as follows:

The disc is supported at its opposite edges where it rests, between the forward surfaces of the ends of the bridge or of the adjacent sleevelike insulation and the rearward surfaces of the cap. Where a ring and tang are used, such as shown at 43 and 44, the disc may rest between the rearward surface of the ring and the forwardly-facing surface of the ends of the bridge,

leaving the central portion free to convex as seen in Figure 2 and free to convex in a reverse direction, i. e., rearwardly when the plunger 58 is pressed rearwardly. l

The front part of the casing is bored at 55 to receive the push button 60 and is eounterbored at Bi and again at 62 to provide shoulders 63 and 42. The button is hollow at 64 for movement of the plunger 58 and its collar 65 against the compression of spring B6. The button is internally threaded to receive a ring 6'! which holds collar 65 in placed. The button may be externally threaded for a flange 68 to engage shoulder 63.

The plunger is forwardly extended as a guide 69 to fit within the spring 66.

Pressing the button rearwardly causes the rear end of the plunger to press the disc rearwardly, convexing the disc rearwardly against the resistance of the retracting spring 49.

Figure 2 corresponds generally with Figure 2, including in this correspondence the entire front end of the switch, of which a portion only is shown. They show the same means for holding and for grounding the disc and the same arms upon the disc. However, the contact pads 58 and 51, if used, now appear on the adjacent faces of the two arms instead of outwardly facing away from each other, as seen in Figure l2.

The contact strips (Bi' only being shown) are now inwardly turned toward each other and receive the contact from the outsides of the contact strips.

In Figure 2b the spring G8' fits within recesses 14 and Hi in the button 80 and plunger 58' limited in movement by ring 582.

The contact strips can be, of course, interior-A ly supported as in Figure 12* resting against and supported by the outer surface 1i of the rearward part of the bridge. In Figure 2* however, the contact strip is not supported against the bridge giving more resilience to permit lateral movement.

In Figures 'l and 12 the contact strips are supported against an interior insulation wall but the switches are normally open. In Figure 2. the strips are not wall supported, but the switch is normally open.

In Figures 2, '7* and 12 mally closed, the strips being wall supported in Figure 12 only.

In the wall-supported strips, it is possible to use thinner material for the strips than otherthe switches are norwise, since they willbe judged by their current In the form shown in Figures 6-10 and 7". the structure is closely similar to that in Figures 1 to 5 and 2* and structure of like position and function is therefore marked with the same reference characters as in these earlier numbered. figures except that they are primed or given other indices.

The rear insulation shown as a separate block at. 2,5 in Figure 2 is here shown as part of the same block '25' as'includes the cylindrical wall insulation for the spaces within which contact takes place in both figures. l

'I'he metal of cap 31 is much thicker than in Figures 1-5 and is extended rearwardly much farther as a flange 12 to overlap the sleevelike member. It is frictionally held to the forward end of the block insulation at 13 so that the pressing of these two parts may be used to secure the cap on thev rear insulation and thus seat the disc between the cap and the forward end of the bridge.

The rear block insulation and the cap, as a unit, may be held within the shell or casing by friction or may be secured within it by screws 4i' as in Figure 6.

The proportions and arrangements of the press button, the spring within it and the plunger operated by it are somewhat different and the ground vis substantially that of Figure 4* where the ground is to be used in Figure 'I or in Figure 7*.

In Figure 'I the plunger 583 and its forward guide 69 may lie wholly outside of the hollow push button, the guide being within a rather more extended pusher spring 66. In this form it is desirable that the spring support the guide 69 oi the plunger rather closely to reduce its wobbling and maintain the face of the plunger approximately tangent to the convex face of In Figures 11 to 16, a further slightly diifer-y ent form is shown in which the fixed contacts may be supported against radially outward (switch closing) `pressure by a wall of the block insulation 2i. The cap Il holding the disc in position against the forward ends of the bridge is fitted over a flange upon the front end of the insulation block. It is preferably a tight fit within the casing and may fit tightly upon the block, The form in Figure 12 is nrmally open and that in Figure 12* is normally closed, but in both the same general characteristics are maintained..

` Where grounding of the disc is desired and the shell is grounded, the same type of ring and tang can be used as in Figure 4". Contact is thus maintained between the shell and the disc, effectively grounding both contact arms.

'I'he resetting or retracting spring 48 in this case is mounted upon a forwardly projecting boss 'il at the middle of the forward part of the bridge.

In Figures 7, 7*, 12 and 12'L it will be noted that the bridge is extended solidly against and forms a part of the block insulation at the rear of the switch.

In operation the button ispushed by hand or by any means not shown, to increase the compression of the spring within the button to a point where the pressure of the spring overcomes the forwardly pressing retracting spring and the resistance due to the normal convexity of the disc and throws the disc to a rearwardly convex yposition. In Figure 2 form this means that the arms spread from normally open position, inside the contacts but spaced from them until the pads engage with the fixed contacts.

In Figure 2 the spreading of the arms interrupts the engagement normally present between the movable contact pads and the fixed contacts and opens the circuit or circuits. When the pressure-however created-upon the button is released, the retracting spring throws the disc to a forwardly convex position and the arms and pads are moved toward each other.

In the Figure 7 form the normally open switch is closed when the disc is convexed rearwardly, the pads upon the arms engaging with fixed contacts which are reenforced against being sprung outwardly by resting in contact with the inner surface of the wall of the insulation block.

In Figure 7* the contact pads upon the arms normally rest in contact with the fixed contacts.

These are unsupported, giving opportunity for slight yielding when the contact pressure is applied. When thedisc is convexed rearwardly these contacts are opened.

In Figure 12 the switch is normally open and ,the retracting spring, instead of fitting in a rel cess, surrounds a projection supported by the bridge. The switch is normally open and the xed ,contacts engaged by the pads are supported against the insulation.

In Figure 12 the switch is normally closed as seen. f

In each of these forms the pads are viewed as forming part of the contact arms, unless separately mentioned in the claims. For this reason when the pads upon the movable arms engage the fixed contacts it may be considered either that the arms engage contacts. or that the pads y engage contacts.

It will be evident that the various structures g shown operate to make and break a single circuit concurrently at two points-where there is no grounding of the disc or, where there is grounding of the disc, to make and break two separate outsidev circuits each of which is connected with one binding post or fixed contact and each of which is grounded through the same grounding of the disc. v

It will be evident that the cap retaining means must restrain the movement of the disc sufliciently to make sure that the arms reliably and properly engage the fixed contacts in closed switch position but that these retaining means for the disc must not clamp the disc so as to interfere with proper disc convexing rearwardly and forwardly under the control respectively of the push button and the retracting spring.

It will be evident also that where mechanical means is used to push the button, it is desirable to protect against the mechanical means unduly forcing the parts, the protection intended being that the mechanical means, if it move too far, shall come in contact with the front end of the casing before inward movement of the button has done any harm to the interior of the structure.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

1. In a snap switch, a grounded casing, an insulation block in said casing, fixed terminals and fixed contacts, connected therewith supported in said block, a transverse bridge across the block presenting spaces at the sides of the bridge, the bridge having forwardly facing surfaces, a snap disc grounded on the casing resting upon the surfaces, movable contact arms mounted upon the side edges of the disc and adapted to be rocked away from or toward each other by snapping the disc, the arms passing through the spaces to engage the fixed contacts or disengage from them, insulation means carrying rearwardly facing surfaces adapted to retain the disc against the bridge surfaces, means for causing pressure between the respective surfaces to hold the disc, and a. plunger carried by the front of the casing and adapted to engage the disc.

2. In a, snap switch, an outer casing, a hollow insulation body having a transverse bridge wall and spaces adjacent the sides of said bridge resulting in inner and outer spaced walls, fixed contacts supported by the spaced walls, insulated binding posts connected with the fixed contacts, spring means supported by the bridge tending to press forwardly from the bridge, a disc engaged by the spring means and convexed forwardly by it, a cover for the disc adapted to hold the disc. arms entering the respective spaces, and spread by rearward -nvexing of the disc, contacts carried by the arms adapted to engage and press against the fixed contacts in the direction of a wall, support at one end of the arm movement and resilient plunger means for convexing the disc rearwardly with consequent breaking or making engagement between the movable contacts carried by the arms and the fixed contacts.

3. In a snap switch, a casing, block insulation within the casing comprising a hollow body and a transversely directed bridge providing lateral passages adjacent the bridge, a grounded disc engaging the bridge, a holder for the disc holding the outer edges of the disc, arms connected with the disc and adapted to be separated when the disc is flexed rearwardly, binding posts at the rear, fixed contacts connected with the binding posts and supported by the inner wall of the hollow body, movable contacts carried by the arms and. adapted to engage the fixed contacts and plunger means for flexing the disc rearwardly.

4. In a snap switch, a casing, a block insulation comprising a hollow body having a transverse bridge across the body presenting a relatively concaved front surface across the length of the bridge, a grounded disc upon the bridge normally convexed forwardly, a cap for the body adapted to hold the outer edges of the disc in position, plunger means for pushing the disc rearwardly, arms upon the edges of the disc, movable contacts carried by the arms, insulation at the rear of the casing, binding posts mounted upon the rear insulation and fixed contacts connected with the binding posts, re-cnforced against pressure of the movable contacts by the walls of the interior of the block and receiving the pressure of the arms.

5. In a normally closed snap switch, a hollow insulation body havirig an outer shell and a transverse insulating bridge block, fixed contacts sup- 9. ported by the bridge wallst against inward movement, insulated binding posts connected with the fixed contacts, a spring pressing forwardly from the bridge, a grounded disc normally convexed forwardly by the spring, a cover for the body confining the disc between the bridge and cover against excessive movement, arms connected with the disc and adapted to be thrown away from each other by convexing of,` the disc rearwardly, o

contacts carried by the arms and normally pressing against the fixed contacts, and spring pressed plunger means for convexing the disc rearwardly. l

6. In a snap'switch, a casing, a block insulation comprising a hollow body having a transverse bridge across the body presenting a relatively concaved upper surface across the length oi' the bridge and means for holding a spring to press a disc away from the bridge, a grounded disc upon the bridge adapted to flex about the outer edges of the bridge, a cover mounted upon the body restricting the extent of movement of the outer parts of the disc with respecttovthe bridge, a spring engaging the disc and tending to push it toward the front of the casing," a plunger spring-pressed rearwardly and terminating ring engaging the outer part of the disc Vand the interior of the casing.

l0. In a snap switch, a button, a plunger spring supported in said button, insulation within the casing affording a forwardly facing holding surface and a rearwardly facing holding surface, .means for securing these surfaces in holding positions, a snap disc retained between the surfaces. contact arms extending rearwardly from the edges of the disc into spaces within the insulation, spring means supported by the insulation tending -to fbrce the disc forwardly, xed contacts mounted within the insulation and adapted to be engaged coincidentally and substantially simultaneously by the contact arms at one limit of the stroke of the arms, and an electrical conductor extending from the disc to the casing and including an electrically conducting ring for the purpose of grounding the disc upon the casing.

1l. In a snap switch, a casing, a snap disc, arms connected with opposite edges of the disc, adapted to vlie near together when the disc is forwardly ing in a button so that the plunger may be pressed against the disc and will yield Within the button, arms attached to the edge of the disc, swung away from or toward each other by disc movement and fixed contacts engaged by the arms.

7. In an electrical switch, an electrically conducting casing, insulation within the rear of the casing, binding posts mounted Within the insulation, xed contacts carried by the binding posts and protected by .the insulation, a bridge support extending transversely of the casing and having an opening, a forwardly pressing compression spring within the opening, a disc mounted upon the support, means within the casing for holding the disc against the support, arms carried by Vthe disc and adapted to engage with or disengage from the fixed contacts, a rearwardly pressing plunger adapted to be pushed additionally against or partly released from the disc, and a hollow button enclosing the plunger and adapted to force the plunger against the disc and overcome the expansive effects of the compression spring.

8. In a snap switch, a grounded casing, a snap disc, a support for the snap disc, providing for the movement of the disc necessary to snap from one contact to another, a pair of binding posts, contacts connected therewith, contact arms carried by the edges of the disc and adapted to snap independently and substantially coincidentally into and substantially coincidentally from engagement with the contacts, a ring of electrically conducting materialengaging the disc and a tang upon the ring engaging the interior f the grounded casing.`

9. A hollow hand-pressed button, a spring Within the hollow button, a plunger carried by the button and adapted to compress the spring, when the button is pressed and the, plunger meets opposition, a snap disc against which the plunger is adapted to engage, supports for the disc, contact arms carried by the disc and snapped independently and substantially coincidentally toward or away from each other, according to the extent of movement of the plunger, a spring compressed by rearward movement of the disc, binding posts having fixed contacts, insulation about the arms and disc, a grounded casing about the insulation and an electrically conductconvexed and to be spread when the disc is rearwardly convexed, means for holding the disc, eni gaging the discl at points between the arms, a spring on the normally concave side of the disc adapted to press the body of the disc forwardly, a ring making contact with the disc and leaving the disc within the ring free to flex, xed binding posts for the switch, fixed contacts electrically connected with the binding posts and adapted to be engaged coincidentally and substantially simultaneously by the arms when they are spread and means` electrically connecting the ring and the casing.

12. In a snap switch, a metallic casing adapted to be grounded, a snap switch disc normally convexed forwardly, held inside the casing, permitting the disc to snap axially of the casing, contact arms carried by the disc and snapped in general radial directions inwardly and outwardly with axial movement of the center of the disc, a spring tending to convex the face of the disc forwardly away from the arms, a grounding ring against which the disc is pressed forwardly by the spring, binding posts, fixed contacts connected with the binding posts and adapted to be engaged coincidentally and substantially simultaneously by the arms when the arms are snapped in one direction, a plunger adapted to engage the convexity of the disc and snap the disc rearwardly against the spring, means for operating the plunger and an electrical connection between the ring and the casing.

13..In a spring-pressed switch, a metallic casing, an insulating sleeve within the casing, a bridge across the casing providing side recesses between the sleeve and the bridge and a forwardly facing bridge recess, a spring in the bridge recess, a disc pressed by the spring and adapted to he pushed by it away from the bridge, arms carried by the side edges of the disc and fitting in the side recesses, binding posts at the rear of'the switch, insulation for the binding posts, fixed contacts carried by the binding posts, movable contacts carried by the arms and adapted coincidentally and substantially simultaneously to engage the fixed contacts at one end of vtheir stroke, a button, a spring pressed plunger pushed by the button for pressing the disc toward the bridge, compressing the spring in the recess of the bridge and an electrical connection engaged by the disc and pressing outwardly against the interior of the casing.

14. In a snap switch, a metallic casing, an in- .11. sulating sleeve within the casins having a bridge, across from one side to the other and providinz side recesses between the sleeve and the bridge, a disc in front of the bridge adapted to be pressed toward and from the bridge. an insulation cap `retaining movement of the outer edge of the disc,

arms carried by the disc, movable contacts upon the arms, fixed contacts with which the movable contacts engage independently and substantially coincidentally, spring-pressed metallic plunger means for operating the disc and an electrical connection between the plunger means and the casing.

noBnaT GTON.

Emmons CITED The followinz references are of record in the me oi this patent:

UNITED STATES PATENTS Number Name Date 2,174,868 Coieen Oct. 3, 1939 10 2,301,874 Hetherington Nov. 10, 1942 2.345.240 Cox Mar. 28, 1944 1,935,509 Leesh et al. Nov. 14, 1933A

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