US 3609636 A
Description (OCR text may contain errors)
PATENTED S5928 isn SHEET 1 UF 2 `flu/enfans wh@ a( United States Patent r1113,6o9,636
72] Inventors William J. Kubin 3,327,282 6/1967 Krolak 339/63 La Grange; 3,390,376 6/1968 Nava 339/217 S John K. Cameron, Hillside, both of Ill. 3,452,316 6/ 1969 Panek et al. 339/45 M [2l] Appl. No. 794,548 prima E J h H M Gl ry xammer osep c ynn  Filed Jan' 28 1969 Attorney-Frederick M. Arbuckle  Patented Sept. 28, 1971  Assignee The Bunker-Ramo Corporation Oak Brook m' ABSTRACT: Electrical connectors having a monodielectric construction in which the configuration of engaging end surfaces of contact-supporting dielectric members and the characteristic of the material of the members are such as to  ELECTRICAL CONNECTORS 6 Chimsnrawing Figs' provide a reliable fluid seal while providing rm mechanical  U.S. Cl 339/60 M, contact support. Specific features relate to the provision of 339/217 S risers on one dielectric member which telescope in the ends of [5 l] Int. Cl H011' 13/52 passages on the other, t0 the use 0f a semihard material  Field 0f Search 339/59-61, preferably a polymer material Operable continuously at high 89, 94 217 temperatures, to the elimination of air pockets so as to provide high corona resistance, and to the use of a wave spring ar-  References Cited rangement for obtaining optimum pressure engagement. Con- UNIT ED STATES PATENTS tact retention members are provided having spring fingers of a 3,255,427 6/1966 Yeiser 339/59 hard material engageable with contacts 0f Soft material, per- 2419018 4/1947 Gudie 339/136 M mittng removal and replacement of the contacts without 3,090,937 5/1963 Keith et al. 339/217 s destruction of the retention member 0r the dielectric.
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ELECTRICAL CONNECTORS This invention relates to electrical connectors and more particularly to electric connectors which are rugged in construction and highly reliable in operation under severe environmental conditions, which have a long operating life and which are readily serviceable.
The invention was evolved with the general object of providing connectors suitable for use in aircraft, especially supersonic aircraft. In such applications, reliability is extremely important and environmental conditions are severe, particularly with regard to extremes in temperatures, shocks and vibrations and exposure to fuels, oils, solids and other fluids used in aircra. It will be understood, of course, that although the connectors of this invention were designed for such applications, the principles and features of the invention are not limited thereto and may be used in various other applications.
In general, connectors ofthe type to which this invention relate include pairs of mating electrical contacts supported in aligned passages in dielectric members which are supported within hollow shells of the connector plug and yits receptacle respectively and adapted to be secured together to bring the mating ends of the contacts together, the opposite ends of the contacts being electrically connected to the ends of wire conductors. One difculty with connectors of the prior art arises with regard to the provision of seals between the dielectric members for the purpose of preventing entry of fluids into the space around the electrical contacts and to prevent failure of the connectors or electrical leakage between the several contacts thereof or between the contacts and the outer conductive shells.
It is not possible to obtain proper sealing with ceramics or other hard dielectric materials. Elastomeric dielectrics or elastomeric seals bonded to dielectric members of ceramic material or the like have been proposed, but severe difficulties have been encountered with regard to swelling and deterioration of elastomeric materials and problems have been encountered with respect to corona discharges. Difficulties have also been experienced with regard to servicing of prior art connectors. Usually, the failure of one contact in a connector has required that the entire connector be scrapped.
An object of this invention is to provide electrical connectors which overcome the disadvantages of prior art connectors and in'which environmental sealing is obtained in a highly reliable manner despite extremes of operating conditions.
A more specific object of the invention is to provide electrical connectors wherein the entire dielectric insert of both the plug and the receptacle may be homogenous throughout and characterized by absence of any type of transverse surfaces, or bonding layers other than at the parting line of separation between the plug and the receptacle while at the same time utilizing no elastomers.
A further object of the invention is to provide electrical connectors which can be readily serviced and in which contacts can be removed and replaced without destruction of other parts.
An important feature of the invention relates to a monodielectric" construction in which each one of a pair of contact-supporting dielectric members is in the form of a single homogeneous member and in which reliable sealing is achieved without the use of separate sealing members bonded to or otherwise associated with the dielectric member. This feature makes possible a simplified and economical construction. It also makes it possible to eliminate the use of elastomers in the connector and eliminates the problems encountered with the use of elastomers.
ln accordance with this feature, the dielectric members along the parting line between the plug and its receptacle have end surfaces which are held together in pressure engagement when supporting shells are secured together and the contiguration of the end surfaces and the characteristics of the material of the dielectric members are such as to provide a highly reliable fluid seal about aligned contact passages in the dielectric members while at the same time providing rm mechanical support for the contacts.
According to a specific feature of the invention, each of the dielectric members is of a substantially homogeneous semihard material, i.e., a material having an elasticity which is less than that of elastomers while being greater than that of ceramic materials, examples of preferred semihard materials being set forth hereinafter.
According to another specific feature of the invention, the end surfaces of the dielectric members include planar portions of substantial areas in surrounding relation to the contact passages, such planar portions being firmly engaged when the shells are secured together and being operative to prevent the formation of fluid-entrapping pockets so as to prevent corona discharges.
A further specific feature relates to the formation of the end surfaces of one or both of the dielectric members with an integral riser about one end of each pair of aligned contact passages, the riser being adapted to telescope within an end portion of the other passage. Preferably, an outer surface portion of the riser and an inner surface portion of the other passage are in pressure-sealing engagement. One of the interengaged surface portions is preferably frustoconical in shape to facilitate alignment and sealing. Most preferably, the outer surface of the riser is frustoconical and the riser is surrounded by a planar surface portion, with dimensions such that the highest pressure is applied at the base of the frustoconical surface of the riser while also applying substantial pressure between the interengaged planar surfaces. Together, these features ensure against formation of fluid-entrapping pockets and prevent corona discharges while providing a highly reliable seal.
Another feature relates to a coupling ring and spring assembly for providing the required pressure engagement between the end surfaces of the dielectric members. Preferably, the coupling ring and one of the shells have stop surfaces of which interengage in a manner to cause the spring means to exert a predetermined engagement force between the end surfaces of the dielectric members. The arrangement serves to maintain a highly reliable seal despite shocks and vibrations and despite expansion and contractions caused by temperature variations.
A further important feature of the invention relates to the locking of a contact member in a passage of a dielectric member by means yof a retention member having spring fingers, the retention member being of a hard metal material and the contact being of a soft metal material. With this arrangement, the contact can be readily driven out without using special tools and replaced with a new contact. This can be accomplished without destruction of the retention member or the dielectric and it is not necessary to scrap the entire connector. Where special tools are available, the contacts can be removed without destruction and it is preferable that such special tools be used. In many cases, however, they are not available.
These and other objects, features and advantages of the invention will become more fully apparent from the following detailed description taken in conjunction with the accompanying drawings which illustrate a preferred embodiment and in which:
FIG. 1 is a side elevational view, partly in cross section, illustrating a connector constructed in accordance with the principles of this invention;
FIG. 2 is an end view of a receptacle portion of the connector of FIG. l, showing the location of keyways and contacts;
FIG. 3 is a cross-sectional view on an enlarged scale, showing in detail the relationship of portions of mating surfaces of the dielectric members of the connector plug and its receptacle before engagement thereof;
FIG. 4 is a cross-sectional view on an enlarged scale, similar to FIG. 3 but showing the surfaces in initial engagement;
FIG. 5 is a cross-sectional view taken substantially along line V-V of FIG. l, on an enlarged scale and showing the mating surfaces of the dielectric members in pressure engagement and also showing the construction and operation of contact retention members; and
FIG. 6 is a cross-sectional view similar to a portion of FIG. 5, and showing one method of removal of contacts.
Reference numeral 10 generally designates a connector constructed according to the principles of this invention. The illustrated connector l comprises four pairs of mating electrical contacts, one pair of contacts 11 and 12 being shown connected to the ends of wire 13 and 14 in the cross-sectional portion of FIG. l. It will be understood that the principles of the invention may be applied to connectors arranged to connect only a single pair of wires or any desired number of pairs of wires and that the wires may be enclosed within suitable shields or casings to form cables. For instance, a l-inchdiameter insert (such as 38 or 39) will accept 19 size 20 mating contacts.
Contacts ll and 12 are supported in aligned passages 15 and 16 in a pair of dielectric members 17 and 18 which are supported within a pair of hollow shells 19 and 20, respectively referred to hereinafter as plug and receptacle shells. The plug shell 19 is adapted to be secured to the receptacle shell 20 by means of a coupling ring 21 connected to shell 19 through a spring arrangement described hereinafter and having an internally threaded portion 23 engaging an externally threaded portion 24 of the receptacle shell 20. The plug and receptacle shells 19 and 20 are also provided with externally threaded portions 25 and 26 on which cable connectors may be threaded or on which grommet-carrying nuts may be threaded.
In assembly of the connector l0, a portion 28 of the plug shell 19 is inserted part way within the receptacle shell 20 and is rotated, if necessary, until a master key 29, projecting radially outwardly from an intermediate point of the portion 28 is properly aligned with an axially extending keyway 30 formed in the internal surface of the receptacle shell 20. The portion 28 is then moved inwardly to interengage the contacts 11 and 12 and to interengage the threads of the portions 23 and 24 after which the coupling ring 21 is turned to fully interengage the contacts 11 and 12 and to provide a seal between the dielectric members 17 and 18 as hereinafter described.
As shown in FIG. 2, four additional polarizing keyways 31-34 are preferably provided in the receptacle shell 20 with corresponding keys being formed in the plug shell 19. Preferably, the master keyway 30 is wider than the additional keyways 31-34 as illustrated. Such additional keys and keyways may be arranged in one of a number of selected pattems to permit the connection of only those plug and receptacle shells having the proper pattern. Preferably, the angular relationship of the keyways 31-34 are changed with respect to the master keyway 30 which has a fixed position relative to the contacts. By way of example, the angles in degrees from the centerline of the master keyway 30 to the centerlines of the keyways 3l-34, measured in a counterclockwise direction as illustrated may be 62, 145, 180 and 280 in one arrangement as illustrated, 79, 153, 197 and 272 in a second arrangement, 135, 170, 200 and 310 in a third arrangement, 49, 169, 200 and 244 in a fourth arrangement, 66, 140, 200 and 257 in a fifth arrangement, and 80, 142, 196 and 293 in a sixth arrangement.
As also shown in FIG. 2, the receptacle shell 20 may be formed with a radially projecting integral plate portion 36 having a generally square peripheral shape and formed with holes for mounting on a panel.
To hold the dielectric members 17 and 18 within the plug and receptacle shells 19 and 20, they are formed with enlarged diameter portions 37 and 38 defining shoulders which are disposed between shoulders 39 and 40 and retaining rings 41 and 42 on the inside of the shells 19 and 20. The portions 37 and 38 may be preferably formed with suitable keys to engage keyways extending into the shoulders 39 and 40 of the shells 19 and 20, to prevent rotation of the dielectric members 17 and 18 relative to the shells 19 and 20.
A seal 44 is provided between the plug and receptacle shells 19 and 20 which is disposed in an annular recess 45 in the inner surface of the receptacle shell 20 spaced a short distance from the forward end of the plug shell 19 when the connector is assembled. The seal 44 comprises an annular member 46 of resilient material, preferably Teflon, which is of U-shaped cross section to define inner and outer walls. Disposed within the member 46 is an annular tubular member 47 preferably of metal and preferably of elliptical cross section which serves to hold the inner and outer walls of member 44 in pressure-sealing engagement with the outer cylindrical surface of the shell 19 and the inner cylindrical surface of the shell 20.
An additional seal is provided between end surfaces 49 and 50 of the dielectric members 17 and 18 and according to an important feature, this seal is obtained with the monodielectic construction in which each of' the dielectric members 17 and 18 is a single homogeneous member, reliable sealing being obtained without the use of separate sealing members bonded to or otherwise associated with the dielectric members 17 and 18. In accordance with this feature, the surfaces 49 and 50 are held together in pressure engagement when the connector is assembled and the configuration of the end surfaces 49 and 50 and the characteristics of the dielectric material are such as to provide a fluidtight seal about the aligned contact passages l5 and 16, as well as the other aligned contact passages, while the contacts are firmly supported in the members 17 and 18.
According to a specific feature, each of the dielectric members is of a substantially homogeneous semihard material, i.e. a material having an elasticity which is less than that of elastomeric materials while being greater than that of ceramic materials or the like.
By way of example, the material of the dielectric members 17 and 18 has a modulus of elasticity on the order of 300,000 pounds per square inch, i.e. from 30,000 to 3 million pounds per square inch, preferably in a range of from 250,000 to 350,000 pounds per square inch. A material which is particularly suitable is a polymer manufactured by the 3M Company and identified as Polymer 360 or P-360." This material and mechanical, electrical, thermal and other properties thereof are described in a paper presented by Morneau and Bringer of the 3M Company at a conference of the Society of Plastics Engineers on Stability of Polymers," at Washington, D C., Sept. 7-8, 1967. ln general, this material is useful over the temperature range of from minus 400 F. to plus 500 F., has good long-term resistance to oxidative degradation and maintains useful structural strength up to 500 F., and it has very good dielectric and other electrical properties. The basic polymer structure consists of phenyl and biphenyl units linked by oxygen and sulfone groups. The nonaliphatic character of this structure is responsible for its resistance to oxidative attack at high temperatures while its aromatic nature contributes to strength at high temperature. The flexural modulus of elasticity of the material varies from about 400,000 pounds per square inch at about 70 F. down to about 250,000 pounds per square inch at 500 F. and the tensile modulus and compressive modulus are comparable.
The polymer 360 material is particularly suitable where the environmental conditions of operation vary widely and especially where the connector must be operable continuously at relatively high temperatures. If the requirements are not so severe, other materials may be used. For example, a semihard rubber material having a modulus of elasticity on the order of 300,000 pounds per square inch may be used when operation at high temperatures is not required.
According to another feature of the invention, the surfaces 49 and 50 include planar portions 5l and 52 of substantial area which surround the ends of the contact passages, the planar portions 51 and 52 being brought into tinn pressure engagement when the connector is assembled and being operable to provide a sealing action and also to prevent the formation of fluid-entrapping pockets. With the use of a semihard material as above described, the surfaces can readily confonn to each other to obtain such results with only a moderate amount of force exerted, while slight inaccuracies in the surface portions can be accommodated.
According to another important feature, the surface 50 includes an integral riser 53 about the end of the passage 16,
adapted to telescope within an end portion 56 of the passage 15, with the outer surface of the riser 53 and the inner surface of the end portion 54 being in pressure-sealing engagement. Preferably, one of such surfaces is frustoconical in shape while the other is cylindrical with the diameter of the cylindrical surface being intermediate the diameters of the frustoconical surface at the opposite ends thereof. This facilitates alignment during assembly while ensuring a pressure seal. Most preferably, it is the outer surface of the riser 53 which is frustoconical in shape and with the base or largest diameter portion of the riser 53 being surrounded by the planar surface 52, the maximum pressure point is at the junction between the planar surface 52 and the surface of the riser 53 so that the formation of fluid pockets is obviated.
The manner of interengagement of the surfaces is illustrated in FIGS. 3, 4 and 5. FIG. 3 shows the relation of the surfaces 49 and 50 before they are brought into engagement, FIG. 4 shows the relation of the surfaces when initial contact is made and FIG. 5 shows the surfaces fully interengaged. lt will be noted that before the surfaces are brought into engagement, the diameter ofthe inner cylindrical surface ofthe end portion 54 is less than the diameter at the base of the frustoconical outer surface of the riser 53, while being greater than the smaller diameter terminal end of the frustoconical surface of the riser 53. Thus with the parts perfectly aligned, the initial contact is at an intermediate point of the frustoconical surface of the riser 53, as shown in FIG. 4. Due to the fact that the diameter of the frustoconical surface of the riser 53 at the terminal end thereof is less than the diameter of the inner cylindrical surface of the portion 54, slight inaccuracies in alignment can be accommodated and the surfaces are moved into proper engagement when moved together. As shown in FIG. 5, when the surfaces 49 and 50 are fully interengaged the riser 53 is deformed at the base portion of the frustoconical surface thereof and there is also a deformation at the end of the inner l surface of the portion 54, resulting in increased pressure and a tight fluid seal. It should be noted, also, that the planar surface portions 5l and 52 are brought into pressure engagement so that there can be no fluid-entrapping pockets in which corona discharges might occur.
The overall result is a highly effective and reliable fluid seal about each of the pairs of mating contacts, it being noted that the telescoping riser arrangement is provided about each of the pairs of mating contacts of the connector.
A further feature of the invention is in the provision of a spring arrangement for obtaining optimum pressure engagement between the surfaces 49 and 50 of the dielectric members 17 and 18. In accordance with this feature, an annular wave spring 56 is disposed between an outwardly extending integral annular flange 57 of the plug shell 19 and an inwardly extending integral annular flange 58 of a member 59 which, for convenience in assembly, is threaded into the coupling ring 21, the member 59 and the flange 58 thereof being rigidly secured in the ring 21 after assembly. The wave spring 56 is of a type known in the art and is formed with several undulation to' engage the flange 57 at several equiangularly spaced points and tol engage the flange 58 at a like number of equiangularly spaced points.
Before assembly of the connector, movement of the flange 57 away from the flange 58 is limited by an inwardly extending integral annular flange 60 of the coupling ring 21. In assembly, the keys and keyways are aligned and the mating contacts are brought into initial engagement after which the coupling ring 2l is rotated to be screwed onto the receptacle shell 20, bringing the contacts l1 and 12 and also the sealing surfaces 49 and 50 into full engagement. Movement of the coupling ring 21 is limited by engagement of the flange 60 with the end of the receptacle shell 20 and metal bottoming action results, the torque required to turn the coupling ring 21 quickly escalates and can be readily felt by the operator so as to indicate by feel that the connector is fully mated.
When so mated, the wave spring 56 exerts the required forces to obtain optimum pressure-sealing engagement between the surfaces 49 and 50. It should be noted that due to differences in temperature coefficients of expansion and contraction, the force exerted may vary to a small degree but the relative dimensions are such as to maintain the forces within an optimum range of values.
With regard to dimensioning, it is noted that the configuration of the end surfaces 49 and 50 of the dielectric members 17 and 18 is important, particularly with respect to the telescoping risers and with a semihard material having characteristics as above set forth, the outside diameter of the dielectric members 17 and 18 may be on the order of l inch and other dimensions are in the same proportion as illustrated in the drawings.
As shown in FIG. 5, the contact 1l is in the form of a male contact having a reduced diameter portion 62 extending within an opening 63 in a main conductive body part 64 of the female contact 12. The body part 64 is formed with a pair of diametrically opposed slots to provide a pair of tines engaging the portion 62 of the contact 11. An auxiliary pressure band 66 is disposed around the tines so formed and a shroud 67 is preferably disposed around the portion of the body 64 having the opening 63 and slots 65 therein. Preferably, the terminal end of the portion 62 of contact 1l is beveled or pointed, the terminal end of the shroud 67 is turned inwardly and a frustoconical surface 68 is formed in the passage 15, extending inwardly from the portion 54, with the relative size and dimensioning being such that the contacts l1 and 12 will engage and mate even though bent out of position when the connector is assembled.
It may be noted that a dual spring action results from the combination of the tined construction and the pressure band 66, the tined construction providing a soft spring action which encompasses the complete maximum deflection range while the band 66 provides a hard spring action to produce adequate force for minimum deflection range. The shroud 67, which may be of stainless steel, limits the deflection of the tines and provides a closed entry restriction for oversized probes.
An important feature of the invention relates to the locking of the contact members in the passages of the dielectric members in a manner such as to permit removal and replacement of contacts without destruction of parts and without requiring the scrapping of an entire connector, plug or receptacle. The illustrated contact 1l is held in place by means of a retention member 70 surrounding a portion of the contact 11 and having an annular groove in its outer surface which receives an inwardly extending annular projection fonned in the contact passage 15. Movement of the contact l1 to the right as illustrated in FIG. 5 is limited by engagement of an annular flange 73 of the contact 11 with one end of the retention member 70. To limit movement in the opposite direction, to the left as viewed in FIG. 5, the retention member 70 has a pair of diametrically opposed slots to define a pair of spring tines or fingers 74 each of which is formed with a shoulder on the inside thereof for engaging a shoulder 76 formed on the contact 1 1.
In assembly, the retention member 70 is first installed after which the contact 1l is inserted from the left, as viewed in FIG. 5, the spring tines or fingers 74 of the retention member 70 being engaged initially by a frustoconical surface 77 of the contact l1. When the contact 1l reaches a position as illustrated in FIG. 5, the fingers 74 spring inwardly to engage the shoulders 75 thereof with the shoulder 76 of the contact 1 1.
ln accordance with a specific feature, the retention member is formed of a relatively hard spring metal while the contact l l is formed of a soft conductive metal. With this feature, the contact 11 may be removed with simple tools, one method of removal being shown in FIG. 6. In particular, an instrument 79 which may be a suitable punch, nail or other similar object may be placed against the end of the contact ll and with a sharp blow, the contact 11 may be moved to the left. With the fingers 74 being of a hard material and with the contact ll being soft, the shoulders 75 may scrape or cut out portions of the shoulder 76 and then ride up on the contact 11 as shown in FIG. 6 which also shows chips 80 of the metal of the contact l l, cut away by the action of the shoulder 75.
It will be appreciated that the sharp blow required for such removal is much greater than would be encountered in operation of the connector, but can be applied when removal and replacement of the contact is required. It is important to note that the retention member is not damaged, nor is the dielectric member 17 damaged, by contact removal and it is not necessary to scrap the entire connector plug.
The construction is such that the contacts can be removed using handtools which slide in and engage the fingers 74 to move them outwardly in which case the contacts are not damaged. The use of such handtools is preferred when they are available. In many cases where it is desired to remove and replace contacts, however, such handtools are not conveniently available. The contact l2 may be held in place by means of a retention member 8l identical to the retention member 70 and operable in a manner operable and identical thereto. It is noted that the male and female or pin and socket connectors ll and l2 along with their respective dielectric bodies may be reversed relative to the plug and receptacle shells 19 and 20. Thus the male or pin contacts 1l may be disposed within the receptacle shell and the female or socket contacts 12 may be disposed within the plug shell 19. In this connection, it is noted that the positions of the enlarged diameter portions 37 and 38 of the dielectric members 17 and 18 and the positions of the shoulders 39 and 40 and retainers rings 4l and 42 are the same relative to the ends of the shells.
It is additionally noted that although not forming part of the present invention, special seal members 83 and 84 are provided around the wires 13 and 14 in the passages 15 and 16 and similar members are provided about the other wires.
It will be understood that modifications and variations may be effected without departing from the spirit and scope of the novel concepts of this invention.
We claim as our invention:
1. ln an electrical connector, a pair of dielectric members, a pair of hollow shells supporting said pair of elongated dielectric members therewithin and arranged to be secured together to hold end surfaces of said dielectric members together in pressure engagement, said pair of dielectric members having one or more pairs of aligned passages therethrough, contacts supported in said passages and adapted to be brought into mating electrical contact when said end surfaces are brought together in pressure engagement, said end surfaces of said pairs of dielectric members including planar portions of substantial areas in surrounding relation to said passages, said end surfaces further including a frustoconical integral riser about one end of a passage of each pair of aligned passages to telescope within a generally circular end portion of the other passage and to engage the dielectric member of said other composed of homogeneous monodielectric material, and
locking means for securing said dielectric members firmly together to deform the base portion of said riser and the portion of its mating dielectric member engaged by said riser, and to maintain said planar portions firmly engaged when said shells are secured together to prevent the fonnation of fluidentrapping pockets, an outer surface portion of said riser and an inner surface portion of said end portion of said other passage being in pressure sealing engagement when said shells are secured together.
2. In an electrical connector as defined in claim l, each of said dielectric members being of material having a modulus of elasticity on the order of 300,000 pounds per square inch.
3. In an electrical connector as defined in claim l, each of said dielectric members being of a polymer material having a basic polymer structure consisting of phenyl and biphenyl units linkedb oxygen and sulfone grougx.
4. In an e ectrical connector as de ed in claim l, said locking means including a coupling ring, spring means acting between said coupling ring and one of said pair of shells, said coupling ring and the other of said pair of shells being adapted for threaded interengagement to cause said spring means to exert a force urging said end surfaces of said dielectric members into pressure engagement.
5. In an electrical connector as defined in claim 4, said coupling ring and said other of said pair of shells having interengaging stop surfaces to limit relative movement and to cause a predetermined engagement force to be inserted between said end surfaces of said dielectric members.
6. In an electrical connector, a dielectric member having a passage therethrough, a contact member in said passage having an annular should between the opposite ends thereof, a retention member around said contact member within said passage, interengaging means between said retention member and said passage for locking said retention member against movement along said passage, said retention member being of a hard spring metal and having spring finger means with shoulder means lockingly engaging said contact member at its said annular shoulder to retain said contact member, said contact member being of a soft conductive metal relative to said metal of said retention member, and said shoulder of said contact member being inclined toward the end portion of said contact member to guide said finger means to ride up onto and cut into said inclined shoulder when said contact member is forcibly driven out from said retention member without damage to said retention member or said dielectric member.