3 1 2 9 5 , 5 1 4 United States Patent Office Patented Jan. 3, 1967 3,295,5 14 ELEC TRICAL DENTAL INSTRUMENT ASSEMBLY Dale E. Hein and William R. Heathe, both of York, Pa., assign ors to The Dentists Supply Company of New York, York, Pa., a corporation of New York 5 Filed June 8, 1964, Ser. No. 373,452 12 Claims. (Cl. 128-2.1) This invention relates to a plural interchangeable electrical dental instrument assembly for use in various elec- 10 trical dental functions such as tooth and oral examination, pulp testing and oral cauterizing. It is the primary object of this invention to provide in a single dental installation, a plurality of different dental instru ments each requiring for its operation a different 15 type of electrical current and a single common head or body member to which each such instrument may be selecti vely and individually connected and by virtue of such connection supplies to the attached instrument the specifi c current that it requires. 20 Anoth er object of this invention is to provide the common head or body member and each of the instruments to be attached thereto with a complemental interfitting multicontact engaging connection wherein the contacts of each instrument and that of the head member en- 25 gage each other in predetermined indexed registry; the contac ts of the head member each supplying a different type of electrical current while in each instrument only one of the corresponding contacts is electrically connected to the operating part or tool of the instrument and the 30 other contacts thereof are free of any connection, such that in the attachment of any selected instrument with the common head member all of the contacts will interengag e in indexed registry with the electrically connected contac t of the instrument engaging the specific contact 35 of the head member supplying the current requisite for the operation of the tool on the selected instrument. A further object of this invention is to provide a multicondu ctor electric -cable including a ground conductor and other conductors each supplying a different value of 40 electri c current, the cable bein- connected to the common head member with each current carrying conductor conne cted to a predetermined contact thereof and with the ground conductor connected to a metal part of the head member. 45 Anoth er object of this invention relates to forming at least part of the casing of each instrument of metal with the electrical operating part or tool thereof grounded theret o and in providing the complemental interfitting connectio n between each instrument and the common head 50 memb er with a movable metal locking member that will groun d the metal part of the @instrument casing with the metal part of the head member to which the ground conductor is connected. Still anotber object of this invention is to so design 55 the common head member, the casing of each of the dental instruments and the movable locking member as to provide a slender, hand-held instrument of great simplicity that is light in weight, easy to assemble and to manip ulate and that is practical and efficient. 60 A still further object of this invention relates to the safety feature arising from the indexed registery of the intere ngaging contacts in the connection of any one of the plural dental instruments with the common head member which safeguards the patient in that the proper cur- 65 rent is always supplied to the selected instrument when attach ed to the head member and the change from one instru ment to another requires no manual adjustment of any voltage control or other electrical apparatus. These and other objects and advantages of the inven- 70 tion will become apparent from the following detailed descri ption of a preferred embodiment when taken in 2 conjunction with 'the accompanyin- drawings in which FIG. 1 is a longitudinal sectional@view of the common head or body member with attached electrical cable taken on line 1-1, FIG. 2, FIG. 2 is an end elevational view of the common head member showing the arrangement of the contact pins. FIG. 3 is a transverse sectional view taken on line 3-3, FIG. 1. FIG. 4 is a cross-sectional view of the multi-conductor cable taken on line 4-4, FIG. 1. FIG. 5 is a longitudinal sectional view of a pulp testing instrument with plug portion thereof taken on line 5-5, FIG. 6. FIG. 6 is an end elevational view of the pulp testing instrument showing the contact socket arrangement as seen from the righthand end of FlG. 5. FIG. 7 is an elevational view showing the pulp testing instrument connected to the common head or body member. FIG. 8 is a longitudinal sectional view of an examination light instrument with the plug portion thereof, taken on line 8-8, FIG. 9. FIG. 9 is an end elevational view of the examination light instrument showin.- the conta-et socket arrangement as seen from the right-hand end of FIG. 8. FIG. 10 is a longitudinal sectional view of a cautery instrument with the plug portion thereof, taken on line 10-10 of FIG. 1 1. FIG. 11 is an end elevational view of the cautery instrument showing the contact socket arrangement as seen from the righthand end of FIG. IO. The plural electrical dental instrument assembly as illustrated in the drawings and described in detail hereinafter consists of a common head or body member 20, FIG. 1, to which is selectively attached one of a plurality of instruments such ias a pulp tester, FIG. 5; an examination light, FIG. 8; or a cautery handpiece, FIG. 10. These instruments are selectively employed for individual connection to the common head member and each when connected becomes electrically operative for its intended purpose and together with the head member provides a manipulative hand-held instrumentality as shown in FIG. 7. THE COMMON HEAD OR BODY MEMBER The common head or body member 20 shown in FIGS. 1-4 comprises a tubular metal housing 22 that is slightly tapered toward its rear end as at 24 and is interiorly formed to provide a forward internally threaded portion 26, an intermediatecylindrical portion 28 and a rear passage portion 30 of a diameter less than the intermediate portion 28. The interior portions 26, 28, 30 of the housing are coaxial with the intermediate por-tion 28 of a greater length than the forward a@nd rear portions. Provided at the adjacent ends of the intermediate and rear portions 28, 30 is a frusto-conical shoulder 32. Connected to the tapered end 24, is a multi-condiictor electric cable 38 which includes a ground conductor 40, a pulp test conductor 42, a cautery conductor 44 and an examination light conductor 46, see FIG. 4. Preferably the cable 38 is covered with a nylon braid covering 48. One end portion of the cable 38, with a short length of the terminal end of each of the conductors exposed, is initially inserted through the tubular housing 22, and has fitted thereon a i-ubber sleeve 50 provided with a forward enlarged flanged head 52 and a rear tapered end 54. Disposed between the cable 38 and the inside diameter of the flanged head 52 is a metal ring 56 for a purpose to be hereinafter described. As seen in FIG. 1, the terminal end 58 of the cable 38 projects forwardly beyond the rubber sleeve flange 52 and the forward edge of the metal ring 56 lies flush with the forward face of the flange 52,

3 the metal ring 56 preferably engaging both the cable 38 and flange 52 in a friction-tight fit. Positioned over the cable terminal end 58 is a metal collar 60 having a rearwardly extending.thin walled sleeve 62 which completely receives therein the enlarged flanged head 52 of the rubber sleeve, with the forward face of the flanged head abutting the inside face of the collar. The free terminal end of the extended sleeve 62 is crimped as at 64 over the rear edge of the flange 52 which is of frustoconical shape, the metal ring 56 serving as an abutment anchor for the compression of the flanged head and relieving the cable of any compressive forces. The crimped end 64 of the sleeve 62 thus provides a metallic shoulder complemental to the shoulder 32 and has seating engagement thereon for a purpose to be hereinafter described. It will be noted that the metal collar 60 with sleeve extension 62 has an outside diameter such as to have an easy sliding fit within the intermediate cylindrical portion 28 of the housing 22 and that when the crimped end 64 is seated on the shoulder 32 the tapered end portion 54 of the rubber sleeve 50 wiU project rearwardly outwardly of the tapered end 24 of the housing 22. The tapered end 54 of the rubber sleeve functions as a guard for the cable 38 preventing undue flexure and possible breaking of the cable at the tapered elid of the housing. Provided in the forward face of the metal collar 60 is an annular groove 66 and a substantially radial connecting grdove 68 for receiving therein the exposed terminal end 70 of the ground conductor 40, see FIG. 3, which is permanently secured to the metal collar by soldering. Carried within the intermediate cylindrical portion 28 of the housing 22 is a cylindrical insulator body 76 formed of any suitable plastic such as melamine and of an outside diameter such as to have a sliding fit within said intermediate portion. Provided at the rear end of the insulator body 76 is a cylindrical recess defining a pocl@et 78 for receiving the terminal ends of the current-carrying conductor 42, 44, 46 of the cable 38. Formed in the insulator body 76 are tbree longitudinal bores 80, 82, 84, parallel to the axis of the insulator body 76, and which extend completely therethrough as shown. Each bore is formed with increased diameter end portions to provide a front and rear shoulder, and the bore 80 is of a larger diameter than the other two bores 82, 84 which are of the same diameter. Disposed respectively within the bores 80, 82, 84 are metal contact pins 86, 88, 90, pin 86 being of a larger diameter than the others. Each contact pin includes base 94 corresponding in diameter to its respective bore and is provided with a flange 96 adjacent its rear end adapted to seat on the rear shoulder of its associated bore, see FIG. 1. Provided on each contact pin is a flange 98 which lies in the plane of the forward face of the insulator body 76. A spring lock 100 is fitted between the flange 98 of each contact pin and the front shoulder of its associated bore for locking the contact pin against axial movement relative to the insulator body. It will be noted that the contact pins are arranged 120' apart, see FIG. 2, and are each of a length such as to project forw@rdly from the insulator body into the forward interiorly threaded portion 26 of the housing and slightly beyond the terminal forward end of the housing 22. Prior to placement of the contact pins within their respective bores each has secured thereto the exposed terminal end of a current conductor of the cable 38. Thus , provided axially in the base 94 of eacli contact pin is a hole 102 into which is inserted the exposed terminal end of a current conductor which is soldered therein to effect a permanent connection. Accordingly it will be seen that the cautery conductor 44 is connected to the larger con - tact pin 86, the pulp test conductor 42 is connected to the contact pin 88 and the examination light conductor 46 is connected to the contact pin 90. To secure the insulator body 76 with attached contact pins in position within the housing 22 there is provided 3,295,514 4 an extemally threaded metal sleeve 106 that is threaded into the forward interiorly threaded portion 26 of the housing. The sleeve 106 is provided at its rear end with an inwardly directed radial rear flange 108 and at its outer end with an outwardly directed radial forward flange 110, the sleeve 106 being of such a length that when the rear flange 108 abuts the forward face of the insulator body to clamp the same along with metal collar 60 to the housing 22, see FIG. 1, the forward flange 110 will be axially 10 spaced from the -'Lorward terminal end of the housing 22. It will be noted that the contact pins extend partly into the sleeve 106 which provides a socket for the reception of an instrument plug as will be hereinatfer described. Carried by the socket sleeve 106 is a metal coupling nut 15 114 of cylindrical form provided with a central threaded portion 116 and having at its rear end a radial flange 118 of a width corresponding to the thickness of the housing 22 and of an inside diameter such as to slidably and rotatably fit on the sleeve 106. The nut 114 includes a rear 20 shroud 120 that overlaps the exterior cylindrical surface of the housin.- 22 for all po8itions of the nut on the sleeve 106, the sleeve flange 110 and the forward terminal end of the housing 22 serving as limit stops engageable by the nut flange 118. A shorter nut-like shroud 122 ex25 tends forwardly of the threaded portion 116 to overlie a cylindrical portion of the casing surface of an instrument as will be hereinafter described. To facilitate manipulation of the coupling ntit 14, the extension surface thereof is fluted as at 124. 30 The multi-conductor cable 38 at its other end is connected to a power unit 126, see FIG. 1, which will supply between 500 and 1000 volts to the pulp tester conductor 42; about 31/2 volts to the cautery conductor 44; and about 2 to 21/2 volts to the examination light conductor 35 46, all for a purpose as will hereinafter be described with regard to the corresponding instruments. THE PULP TESTER 40 Illustrated in FIGS. 5 and 6 is a pulp test instrument 130 wmch has for its purpose the testing of the vitality of a tooth. In an instrument of this type and purpose a high voltage is necessary because of the possibility . of classifying,a non-vital pulp as vital, a common occurrence in pulp testers employing a low voltage. In the herein de45 scribed pulp testing instrument, an exemplary average operating current of about 600 volts is required for its normal operation but higher voltage is available. In the construction shown, the pulp test instrument 130 inc des a tool consisting of an elongated tapered probe tip 132 r'O of plastic such as melamine or any other suitable plastic material provided with a stainless steel core rod 134 projecting outwardly as at 136 from the probe tip. Fitted over the rear end portion of the probe tip is a r,,5 tapered tubular metal front body 138 which in tum carries at itS Tear end the forward end portion of a tubular Plexiglas member 140 having an intermediate annular lens portion 142. A tapered tubular metal rear body or sheath 144 having an internally threaded portion 146 is 60 fitted over the rear portion of the Plexiglas member 140 with the threaded portion 146 engaging the threaded portions 148 of the Plexiglas member 140. As will be seen from FIG. 5, the adjacent terminal ends of the front and rear metal bodies abut the annular lens 142, the outer surface of which extends slightly beyond the tapered outer 6,5 surface of the front and rear metal bodies. Contained within the Plexigla-s member 140 is a neon bulb 152 baving two leads 154, 156. Lead 154 extends forwardly of the neon bulb 152 and is @connected to a helical compression spring 158 which engages the inner 70 terminal end of the stainless steel core rod 134. The@ other lead 156 is soldered to a metal block 159 that fits within and seats on the rear terminal end of the Plexiglas member 140 in the manner shown. The probe tip 75 132 and Plexiglas member 140 are secured in any desired

5@ manner as by an epoxy adhesive to the front metal body 138. The rear end portion of the rear metal body 144 is provided with an outer cylindrical portion 160 and an outer threaded end portion 162 for a i)urpose to be hereinafter described. The metal block 159 provides an end wall of a cylindrical recess 164 at the end of the rear metal body 144. A plastic base member or plug @dapter 168 of melamine or other suitable plastic, provided with an intermediate annular flange 170, is secured in position within the cylindrical recess 164 by an epoxy adhesive or in any other desired manner, the flange 170 abutting the end portion 162 as shown. The portion of the plug adaptor extending rearwardly of the flange 170 constitutes a plug 172 that is dimensioned to fit within the socket gleeve 106 of the head member 20. Fixedlysecured within the plug 172 in a manner similar to that of the contact pins 86, 88, 90 are three metal contact sockets 176, 178, 180 arranged 120' apart, and each is parallel to the axis of the plug adapter. T'he contact sockets 176, 178, 180 are each complemental to the contact pins 86, 90 and 88 respectively of the common head member 20. Contact @socket 180, see FIG. 5, includes a spring pressed metal button 182 that bears against the face of metal block 159, and will thus conduct current to the neon bulb 152. In this respect contact socket 180 is a "live" socket and will bereinafter be referred to as such. The other two contact sockets 176 and 178 have no electrical connection whatsoever with the operating parts of the pulp tested instrument and are in this respect "neutral" and will hereinafter be referred to as such. Thus, it will be seen that, with the plug 172 plugged into the socket sleeve 106 of the head member 20, there can only be one predetermined position thereof with respect to the head member 20 by virtue of the mating interengagement of the larger diameter contact i)in 86 with the lar,-Cr diameter contact socket 176, and accordingly only the requisite exemplary current of about 600 volts supplied by the pulp test conductor 42 will be transmitted from contact pin 88 to the "live" contact socket 180 to effect operation of the pulp test instrument. The other two contact sockets 176, 178 being "neutral," their mating engagement with current carrying contact pins 86 and 90 respectively will have no effect. It thus is seen that the described contact pins and contact sockets make up a pattemed arrangement, with the corresponding contact pin 86 and contact socket 176 being of larger size than the other providing for an indexed registry of the pulp test instrument 130 with respect to the head member 20 in its connection thereto. It is to be understood that, with plug 172 pluggedinto socket sleeve 106 of the head meniber 20, both the pulp test instrument 130 and head member 20 are securely held together by the threaded engagement of the coupling nut 114 with the tbreads 162 on the rear metal body 144, the forward shroud 122 of the nut riding on and overlapping the cylindrical portion 160 of the rear body 144; the joined pulp test instrument and head member being shown in FIG. 7. It will be apparent that the combined instniment of FIG. 7 is so dimensioned as to be easily hand-held and is manipulatable to any desired position in the use thereof. In the connecting together of the pulp test instrument with the head member 20 by threading of the metal coupling 114 on the threads 162 of the rear metal body 144, the rear metal body 144, which in effect constitutes a handle for the pulp test instrument, is @rounded to the ground conductor 40 throu,@h the metalto-metal contact of nut 114, slee-ve 106, housing 22 @Lnd roetal collar part 60 of th, head member, see FIG. 1. , In the use of the pulp test instrument the circuit is completed by the dentist or operator holdin@ the instrument a.-ainst the tooth to be tested and touching the patient bodily. To indicate that the pulp test instrtiment is opera3,295,514 6 tive the neon bulb 152 will light iip and the light will thus be visible through the annular lens 142. TWs construction is but one of a number of different types of indicating means which may be used for purposes of permitting ready and visual observation that the circuit in the instrument has been completed and that the instrument is functioriing. THE EXAMINATION LIGHT INSTRUMENT In FIGS. 8 and 9, there is illustrated an examination 10 light instrument 190 that requires for its operation an exemplary current of about 2 or 21/2 volts. The examination light instrument 190 consists of an elongated forwardly tapered tubular metal casing or sheath 192 having a central bore 194 therein extending longitudinally from the 15 forward end inwardly, merging with additional stepped bores 196 and 198. Supported at the forward end of the casing 192 is a mirror mount 198 which carries a magnifying mirror 200 disposed at an inclination in iorwardly spaced relation to the front end of casing 192. The rear 20 end of the casing 192 is enlarged and exteriorly threaded as at 202 and formed with a short cylindrical portion 204. Between stepped bores 196 and 198 is an annular shoulder 212 which receives an insulating plug 214 provided with an axial opening 216 which receives and supports the 25 inner end of a contact rod 218 having a head 220 abuttable with plug 214 to limit the movement of said rod in one direction. Preferably press-fitted onto the forward end of rod 218 is an insulating bushing 221 which is movable, guidably, relative to the interior of a metallic lamp socket 30 sleeve 222 whichis press-fitted or otherwise secured to the outer end of casing 192 so as to project beyond the end thereof for a purpose to be described. An internally threaded lamp socket 223 is secured within the outer end of sleeve 222, sucli as by press-fitting it therein, to receive 35 the threaded end of a suitable miniature size electric lamp bulb 224. Positioned and seciired within the rear terminal end portio-@l of the casing 192, by suitable cement or the like, is a base member or plug adapter 168a which is substan4o tially identical in all resi3ects to the plug adapter 168 of the pulp test instrument shown in FIGS. 5 and 6, and has contact sockets 176a, 178a and 180a carried by pltig 172a which correspond in dimensions and arrangement with the contact sockets 176, 178 and 180 carried by plug 172 45 of plug adapter 168. In the examination light instrument 190, contact socket 178a is the @'live" contact socket while the other two contact sockets 176a and 180a are "neutral." Plug adapter 168a has a plurality of bores formed in the inner end thereof and into which the various contact 50 sockets 176a, 178a and 180a are pushed for firm seating therein. Within one of such bores 225, a movable contact 226 is mounted forprojection from the inner end of plug adapter 168a. A suitable coil spring 228 within bore 225 iirges contact 226 outwardly into contact with head 55 220 of contact rod 218, whereby a circuit is established to supply ctirrent from the "live" contact socket 178a to lamp bulb 224 through theinterengaging spring 228, contact 226, head 220, and contact rod 218, the outer end of which is urged by spring 228 forwardly into contacting en,@age60 ment witb the bottom of base of lamp bulb 224. The shell of the base of lamp bulb 224 is grounded through metal casing 192, thereby completing the lamp circuit. Accordingly, when plug 172a is inserted into socket sleeve 106 of the common head member 20, the indexing 65 registry of the contact sockets with the contact pins will provide that the 2-21/2 volt current supplied by the examination li.-ht conductor 46 of multi-conductor cable 38 will be transmitted through the mating interengagement of contact socket 178a with contact pin 9 ' 0 to transmit the 70 current throtigh coil spring 228 and the circuit-completina members described above extendin.@ ftom said spring to lamp bulb base 220, thereby energizing lamp bulb 224. The contact soclcets 176a and 180a are "neutral" and thus the corresponding mating engagement of the same with 75 contact pins 86, 88 will be of no effect. Mirror 200 in-

7 cludes a split sleeve 230 which frictionally engages sleeve 222 for support thereby. When the plug 172a of instrument 190 is plugged into the socket sleeve 106 of the common head member 20, thecasing 192 and the head or base member 20 are connected together by the coupling nut 114, the threads 116 of which threadably en.- age the outer threads 210 of the housing sleeve 206, with the forward shroud 122 of the, coupling nut riding over and overlapping the cylindrical surface portion 204 of the casing 192. As with the pulp testing instrument 130, the connection of the coupling nut 114 to the casing 192 will effect grounding of the metal casing 192 to the ground conductor 40. Also, as with the pulp testing instrument 130, the joining together of the e-xamination light instrument 190 with the common head member 20 will provide a hand-held assembly similar to that of FIG. 7 and easilymanipulatable in all directions. THE CAUTERY INSTRUMENT In FIGS. 1 0 and 1 1 there is illustrated a cautery instrument 240 that requires for its operation an exemplary current of 31/2 volts. The cautery inst-rument 240 consists of !a tubular forwardly tapered metal casing or shea@th 242 carrying at its forward end an elongated slightly tapered plastic nose piece 244 made of melamine or anY other suitable plastic matorial. Extending longitudinally within the nose piece 244 are a pair of transversely spaced small diameter metal tubes 246, 248. Positioned and soldered within the forward end of each metal tube are metal socket members 250, 252 respectively, the outer ends of which lie flush with the terminal end of @the nose piece. A removable end member 256 of like plastic material carries two rearwardly extending contact pins 258, 260 adapted to respectively mate within the socket members 250, 252. A .tool comprising an exemplary nickel-chromium resistance wire loop provides a cauterizing tip 264, the end of the wire being each Ti.-idly secured to a base of the contact pins 258, 260 by brazing or otherwise. As will be apparent from FIG. 10, the end member 256 is removable to permit tip 264 to be Teplaced, the shape and dimensions of the end member 256 being such as to be coextensive with the outer surface of the nose piece 244 when abutting the terminal end thereof. The inner end of the nose piece 244 is of reduced diameter and is secured within the forward end portion of thecasing 242 by means of an epoxy adhesive or the like. The two metal tubes 246, 248 preferably lie in the same vertical plane @and extend rearwardly beyond the inner end of the nose piece 244 into the casing 242. The end of the upper metal tube 246 is flattened as at 266 to provide a contact and is held @spaced from the end 268 of the lower metal tube 248 by an insulating sleeve 270 surrounding the same. . The rear end portion of the casing 242 is fornied inteTiorly with a cylindrical bore 272 larger in diameter than the central cylindrical chamber 274 to define a shoulder 276. Seated against the shoulder 276 at the inner end of bore 272 is a metal ring 278 that is secured in place by solder or otherwise. The wall of the casing 242 opposite the flattened end 266 is slotted as at 280 to receive thetein a switch button 284 havin.- on its underside a metal contact bar 286. A leaf spring 288 is secured at one end by soldering or otberwise to the metal ring 278 and its other end is secured in metal to metal contact with the contact bar 286, the leaf spring 288 acting to normally bold the switch button 284 spaced from the flattened end 266 which as indicated SeTves as a mating contact. Provided exteriorly at the rear end portion of the casing 242 is a cylindrical portion 290 and a threaded portion 292. Positioned within the bore 272 at the rear end of casing 242 is !a base member or plug adapter 168b identical in all respect to the hereinabove described plug adapter 168 of the pulp test instr-ument of FIGS. 5 and 6, with the contact sockets 176b, 17$b and 180b carried by plu.- 3,295,514 172b, corresponding in dimensions and arrangement with the contact sockets 176, 178, 180 carried by plug 172 of plug adapter 168. In the cautery instrument 240, contact socket 176b is -the "live" contact socket while the other two contact sockets 178b and 180b are "neutral." Thus, a conductor 296 positioned within casing chamber 274 and passing above leaf spring 288 has one terminal exposed end 298 connected to contact socket 176b in any suitable manner and its other terminal exposed end 300 10 inserted into the rear end 268 of lower metal tube 248 and secured therein by soldering or otherwise. Accbrdingly when plug 172b is inserted into socket sleeve 106 of the common head member 20, the indexing registry of the contact sockets with the contact pins will 15 provide that the 31/2 volt current supplied by the cautery conductor 44 of multiconductor cable 38 will be transmitted through the mating interengagement of contact socket 176b with contact pin 86 to transmit the current to the lower metal tube 248 and to the cautery tip 264, 20 the circuit being closed on depression of the switch button 284 to engage contact bar 286 with contact 266 comprising the flattened end of upper metal tube 246. The contact sockets 178b and 180b being "neutralized," the correspon g mat ng engagement of the same with contact 25 pins 90 and 88 respectively will be of no effect. With the plug 172b plugged into the socket sleeve 106 of the common head member 20, the casing 242 and the head member 20 are completely connected together by the coupling nut 114, the threads 116 of which threadably; 30@ engage the threads 292 at rear end of casing 242, with the forward shroud 122 of the coupling nut ridin.- over and overlapping the cylindrical surface portion 290 of the casing 242. As with the above-described pulp test instrument and examination light instrument, the tiahten35 ing of the coupling nut 114 on the metal casing 242 will effect grounding of the casing by coniiection thereof to the ground conductor 40. Siiiiilarly, as with each of said other two instruments, the joining together of the cautery instrument 240 with the common head member 20 will 40 provide a hand-held assembly similar to that of FIG. 7 iand easily manipulatable in all directions. While a preferred embodiment of the invention has been described in detail and illustrated in the alecompanying dr-awings, it is to be understood that the invention contemplates such changes as having a socket sleeve with 45 contact pins at the rear end of each instrument, and providing the head member with a common plug carrying the contact sockets, the pattern arrangement and indexing registry being the same. Also the male and female form of contacts as employed in the prefer-red described em50 bodiment may be replaced with any other suitable type of interengaging contacts. Further, the multi-conductor cable need not carry a different voltage for each conductor but may equally as well carry different currents, i.e., certain conductors may carry A.C. while other con55 ductors may carry D.C., depending upon the type of instrument, its function and current requirement. Accordingly such changes as notedhereinabove and other modifications may be Tesorted to without departing from the spirit of the invention, the scope of which is set forth 60 in the annexed claims. We