EP0190843A1

EP0190843A1 - Improvements relating to electrical connectors

Info

Publication number: EP0190843A1
Application number: EP86300414A
Authority: EP
Inventors: Glynn Evan Phillips
Original assignee: Hellermann Deutsch Ltd
Current assignee: Deutsch UK Ltd
Priority date: 1985-01-22
Filing date: 1986-01-21
Publication date: 1986-08-13
Also published as: GB2211676A; GB8900608D0; GB8601408D0; GB2170364A; GB2211676B; GB2170364B

Abstract

An electrical connector, i.e. a plug, receptacle or adaptor, for use with a single twisted pair screened or double screened cable comprises a triaxial assembly of first, second and third coaxial contacts, the first of which is coaxially embraced by and electrically insulated from the second which in turn is coaxially embraced by and electrically insulated from the third. The triaxial assembly comprised of the first, second and third contacts forms a sub-assembly, with the third contact having a screw-threaded retainer nut on one end serving to retain and operatively position the first and second contacts and associated electrically insulating bushings within the internal void of the third contact. An outer body shell envelops the triaxial assembly and provides mechanical protection and radio-frequency screening therefor. The first and second contacts have axially-offset crimp buckets for connection thereto of the conductors of a single twisted pair screened cable, and the retainer nut associated with the third contact has a rearward tubular projection cooperating with a crimp sleeve for connection thereto of the cable screen. For a double screened cable, the outer body shell can be insulated from the third contact and connected to the outer cable screen.

Description

This invention concerns improvements in or relating to electrical connectors and more particularly, though not exclusively, concerns an improved connector for single twisted pair screened cable applications such as for example in data highway systems where such a cable is commonly employed to address and interconnect a number of remote terminals whose function may have prime importance to equipment survivability and where the connectors correspondingly must be designed for long term reliability.
The invention utilises coaxial connection techniques in a connector adapted and designed for use with single twisted pair cable and, more particularly, though not exclusively, single twisted pair screened cable. In its application to a single twisted pair screened cable, the invention enables the provision of a series of triaxially interfaced connectors comprising free plugs, receptacles and adaptors.
Electrical connectors are known, for example from US-A-4307926, EP-A-67727 and GB-A-2085676, which comprise first, second and third coaxial contacts wherein the first contact is coaxially embraced by and electrically insulated from the second contact and the second contact is coaxially embraced by and electrically insulated from the third contact, the contacts being accessible at one axial end thereof for mating with a complementary connector, conductor fastening means being provided for connection of the conductors of a twin core screened cable to the first and second contacts, and means being provided for connection of the screen of the cable to the third contact. A functionally similar though less sophisticated connector device is also described in GB-A-893239.
The known connectors suffer, to a greater or lesser extent, from being disadvantageously difficult to assemble. In the connector of US-A-4307926, for example, whilst crimping techniques are employed for connecting the cable conductors to the respective connector contacts, different crimp tools are required to be utilised for connecting to the first and second contacts, and the cable conductors have to be cut to different lengths. In the connector of EP-A-67727 the connections of the cable conductors to the first and second contacts are designed to be effected by soldering, which is disadvantageous as compared to crimping, and not only do the conductors have to be cut to different lengths but their bared ends are even required to have different lengths. The connector of GB-A-2085676 is more advantageous in that the connections of the cable conductors to the first and second contacts are crimped connections made with the same crimping tool, but even in the case of this connector the two conductors of the cable have to be dressed to different lengths.
In the connectors of US-A-4307926 and EP_-A-67727 the first or centre contact is restrained against rearward axial movement only by the_' stiffness of the cable conductor to which it is connected. Not only is this disadvantageous in itself, but also in combination with the requirement for the cable conductors to be cut to different lengths the further disadvantage arises that, if the respective conductor is inadvertently cut too short, the centre contact of the connector may not extend forwardly sufficiently far to make a sufficient connection with the respective contact of a mating complementary connector. In the connector of GB-A-2085676 the position of the centre contact within the assembled connector is predetermined by virtue of the arrangement of the connector, which is advantageous as compared with the connectors of US-A-4307926 and EP-A-67727, but if the conductors of the cable were inadvertently to be cut improperly with an incorrect inequality in their lengths then assembly difficulties could arise.
In contrast to the prior art connectors discussed hereinbefore, the present invention provides for the termination of the conductors of a single twisted pair screened cable to first and second, inner and outer contact members of a coaxial contact advantageously by means of crimp buckets or other conductor fastening means forming integral parts of the contact members and adapted for connection to conductors cut to the same length. The screen of the twisted pair cable is preferably terminated at a further contact member which embraces and surrounds the coaxial contact assembly to which the conductors of the cable are terminated and is insulated therefrom so as to constitute therewith a triaxial contact assembly.
In accordance with an exemplary embodiment of the invention as hereinafter described in detail, the first and second contacts of the respective connector each has an integral crimp bucket at its rearmost end with the crimp buckets arranged so that, when the first and second contacts together with associated electrically insulating bushes are sub-assembled, the two crimp buckets are offset one on each side of the axis of the connector and aligned with each other transversely to the connector axis. The crimp buckets are thus readily accessible for termination to the bared ends of the conductors of a twin cable cut to the same length and advantageously can be identical to each other. Having crimped the conductors to the crimp buckets, the sub-assembly thus comprised may be loaded into the third contact with the interpositioning of an insulating bush and captured therein by means of a screw-threaded fastening means adapted to be screw-threadedly secured to the rearmost end of the third contact. The arrangement of the first, second and third contacts, the insulating bushes associated therewith, and the fastening means is advantageously such that the first and second contacts load into the third contact in precisely predetermined positional relationships which are not susceptible to variation either during or after assembly. The fastening means advantageously is formed to be crimped to the screen of a screened cable.
A mating plug and receptacle connector in accordance with the invention will comprise respective male and female contact members designed to join together in the assembled connector, and preferably the two connector parts will each further comprise an outer shell adapted to mate with the outer shell of the other part. The outer shells of respective parts advantageously will be provided with complementary orientation keyways or the like designed to facilitate and ensure correct mating of the respective parts, and by virtue of design variations incorporated into such complementary formations it can be ensured that a particular plug for example can mate with only a respective one of a plurality of adjacently located receptacles, and vice versa. The outer shells could be arranged to be secured together by any convenient means such as for example by means of a bayonet type or BNC style fixing or by means of interengaging screw-threaded parts or by means of fastening clasps or clips.
Such outer shells as are abovementioned advantageously can be arranged to provide mechanical protection for the respective contact assemblies provided therewithin. The contact assemblies can for example be recessed within their respective shells so as to be protected against accidental damage in the event that the respective connector part was dropped or was impacted by a tool for example dropped onto it. The shells can also advantageously provide radio-frequency screening by being formed of electrically conductive material and preferably for such purpose will be arranged to be electrically continuous with the screen of the cable and will be arranged to be secured to the outer shell of a complementary connector by means of interengaging screw-threaded or other parts such as to preclude flexure of the mated interface which could result in loss of screening. Environmental sealing advantageously may additionally be provided by provision of seals at appropriate positions within the connector, and by provision of protective caps for interface sealing in the unmated condition of the respective connector parts.
In an advantageous arrangement the outer shell of one connector adapted to mate with another connector comprises a male part adapted to be received within a complementary female part of the outer shell of the other connector, and an internally screw-threaded coupling ring is affixed to the first-mentioned connector to be rotatable about the axis thereof but to be incapable of axial movement relative thereto. The second connector has a complementary screw thread about the exterior of its female part, so that the two connectors can be mated by engaging the screw-threads of the coupling ring with those on the female part of the other connector and turning the coupling ring so as to urge the two connectors together. With such an arrangement, an elastomeric 0-ring may be made captive within a recess defined between the coupling ring and the respective connector body and can serve the dual functions of providing environmental sealing and also of locking the coupling ring when the two connectors are assembled together, the 0-ring then being subject to axial compressive forces causing it to expand radially thereby frictionally locking the coupling ring to the respective connector body.
For some applications of single twisted pair screened cable, for faster data transmission rates for example, double braided or double screened cables are commonly used and the present invention provides a variant for such cables by provision of an insulator between the triaxial contact assembly aforementioned and the outer shell and providing for the electrical connection of the outer screening braid to the outer shell. With such an arrangement, two discrete screen continuity paths are provided, namely at the triaxial contact assembly and at the outer shell.
A connector constructed in accordance with the present invention can readily be constructed for compliance with accepted military and other standards, for example as regards conductor and screen termination by means of octodent and hexagon crimps. By virtue of this feature, the invention is seen as enabling the provision of a connector meeting the most vigorous requirements.
In addition to plugs, receptacles and adaptors the invention also extends to an impedance matching termination for use with plugs and/or receptacles and/or adaptors in accordance with the invention and which comprises a plug or receptacle in accordance with the invention having connected thereto a terminating resistor rather than a single twisted pair screened cable.
The invention together with further features and advantages thereof will best be understood from consideration of the following detailed description of an exemplary plug and cooperating receptacle in accordance with the invention, and an exemplary adaptor, all as illustrated in the accompanying drawings, wherein:

Figures 1A and 1B respectively show an axial sectional view and an end elevation view of a plug according to the present invention;
Figures 2A and 2B respectively show an axial sectional view and an end elevational view of a receptacle according to the present invention adapted for cooperation with the plug of Figures 1A and 1B; and
Figure 3 shows a part sectional view of an adaptor.

Referring first to Figure 1A, the plug according to the invention comprises a generally tubular plug body 1 which has an internally screw-threaded coupling ring 2 affixed thereto for cooperation with screw threads formed on a body part of the receptacle (to be described), and has at its right-hand end (as viewed in Figure 1) an internally screw-threaded portion for engagement with external screw threads formed on an outer body nut 3 which serves to capture within the internal void of the plug body 1 a triaxial plug contact assembly 4 shown terminated to the conductors and screen of a single twisted pair screened cable 5. The triaxial plug contact assembly 4 comprises a generally tubular outer member 6 which is internally screw-threaded at its right-hand end for cooperation with external screw threads formed on an inner body nut 7 which serves to capture within the internal void of the member 6 a coaxial contact assembly comprising inner and outer contact members 8 and 9 respectively which are insulated from each other and are maintained in operative positional relationship with respect to each other and with respect to the internal bore of the outer triaxial contact assembly member 6 by means of insulating bushes described below.
The left-hand tubular end portion of the outer member 6 of the triaxial contact assembly 4 constitutes a female contact for cooperation with a corresponding male contact provided in the receptacle of Figures 2A and 2B and, as shown, comprises a skirt formed of a plurality of separate contact fingers which are sprung slightly inwardly towards the plug axis and are internally chamfered at their free ends for ease of insertion of the cooperating male contact of the receptacle. The inner contact member 8 of the coaxial contact assembly contained within the member 6 likewise constitutes a female contact for cooperation with a corresponding male contact provided in the receptacle and has a skirt portion formed of a plurality of inwardly sprung contact fingers, and the outer contact member 9 of the coaxial contact assembly constitutes a male contact for cooperation with a corresponding female contact provided in the receptacle. The inner contact member 8 is received within the bore of the tubular outer contact member 9 with an electrically insulating sleeve 10 provided therebetween and at its right-hand end is formed integrally with an off-axis crimp bucket 11 serving as a means for terminating one of the conductors of the cable 5. The outer contact member 9 is mounted within the outer member 6 of the triaxial contact assembly by means of an electrically insulating annular bushing 12 having a left-hand face which abuts an internal abutment 13 of the member 6, and at its right-hand end is formed integrally with a second off-axis crimp bucket 14 serving as a means for terminating the other conductor of the cable 5. A further electrically insulating bushing 15 surrounds and locates the crimp buckets 11 and 14 within the internal bore of the element 6 and is abutted at its right-hand surface by the left-hand end of the inner body nut 7 as it is screwed into the right-hand end of the outer member 6 of the triaxial contact assembly.
By virtue of the above-described construction, the triaxial contact assembly comprising the outer member 6, the inner and outer contact members 8 and 9 of the coaxial contact assembly with their integral crimp buckets 11 and 14 respectively, and the insulating components whereby the inner and outer contact members 8 and 9 are packed and retained within the outer member 6 of the triaxial contact assembly in cooperation with the inner body nut 7, constitutes a separate subsystem of the illustrated plug connector wherein the respective parts are precisely assembled and maintained in operative relationship with each other. The right-hand end of the inner body nut 7 is formed as a tubular rearward projection which cooperates' with a crimp sleeve 16 to enable the cable screen to be terminated to the triaxial contact assembly with the twisted cable conductors passing through the nut 7 and being terminated at the crimp buckets 11 and 14.
The triaxial contact assembly subsystem is arranged to fit closely within the bore of the plug body 1 and with an external shoulder of the outer member 6 of the triaxial contact assembly abutting an internal shoulder within the bore of the plug body 1 to limit the insertion of the triaxial contact assembly into the plug body 1. The outer body nut 3, as aforementioned, has an externally screw-threaded portion which cooperates with an internally screw-threaded portion of the plug body 1 and serves to retain the triaxial contact assembly within the plug body by virtue of a shoulder portion of the nut 3 abutting a surface of the inner body nut 7. An 0-ring seal 17 provides for environmental sealing which can be enhanced as desired by provision of a heat-shrink or elastomeric sleeve 18 engaging an enlarged end portion of the nut 3 and overlying the cable sleeve.
At its forward or left-hand end, the plug body 1 has a nose portion 19 which, as shown, extends beyond the limits of the triaxial contact assembly so as to serve to protect the triaxial contact assembly against scoop or probe damage; it will readily be appreciated that by recessing the triaxial contact assembly in this way with respect to the forward end of the plug, the risk of damage to the triaxial contact assembly is reduced. The extended nose portion 19 of the plug body 1 also serves to ensure that when the plug is being mated with an appropriate receptacle the mating parts necessarily come together coaxially.
The nose portion 19 of the plug body 1 is formed externally with a number of keys 20 (see particularly in Figure 1_B) which are provided so as to ensure that the plug can be mated only with a receptacle (to be described hereafter) having complementary keyways formed in the corresponding female part of its body.
The coupling ring 2 is affixed to the exterior surface of the plug body 1 by means of a circlip 21 engaged with grooves formed internally of the coupling ring 2 and externally of the plug body 1. An O-ring seal 22 is captive within a recess defined between the coupling ring 2 and the plug body 1 and serves the dual function of providing environmental sealing when the plug is assembled with an appropriate receptacle and the seal is subjected to axial compressive forces, and also of locking the coupling ring 2 when the plug is assembled with a receptacle and the axial compressive forces cause the O-ring to expand its radial dimension thereby frictionally coupling the coupling ring 2 to the plug body 1. These features coupled with the use of fine screw threads ensure a secure and vibrationproof coupling of the plug to a respective receptacle.
Other features of the plug will be apparent to the skilled reader from consideration of the detail shown in Figures 1A and 1B and will not be particularly described herein.
Having thus particularly described a plug embodiment of the invention, a receptacle for cooperation with the described plug will hereinafter be described with reference to Figures 2A and 2B.
Referring particularly to Figure 2A, the receptacle as shown comprises a generally transverse tubular receptacle body 30 formed with a square flange 31 for attachment of the receptacle to a bulkhead or instrument panel for example. On the right-hand side of the flange 31, as the receptacle is viewed in Figure 2A, the receptacle body 30 has an externally screw-threaded portion 32 which is provided internally with keyways 33 complementary to the keys provided on the nose portion of the plug body; this portion of the receptacle body constitutes a female connector member for cooperation with the male nose portion of the plug, the external screw threads on the receptacle cooperating with the internal screw threads provided on the plug coupling ring. At its other, left-hand, end the receptacle body 30 is internally screw-threaded for engagement with external screw threads provided on an outer body nut 34 which, similarly to the outer body nut 7 in the aforedescribed plug, serves to capture within the internal void of the receptacle body 30 a triaxial receptacle contact assembly 35 similar in many respects to that provided in the plug but providing complementary contact functions; that is to say, whereas the inner and outer contact members of the coaxial assembly in the plug provide female and male connection functions respectively and the outer contact member of the triaxial plug- contact assembly provides a female contact function, in the receptacle these functions are reversed with the inner and outer contact members of the coaxial assembly in the receptacle providing male and female contact functions respectively and the outer contact member of the triaxial receptacle contact assembly providing a.male contact function. An O-ring seal 36 is provided between the outer body nut 34 and the receptacle body 30 as shown and, as in the plug, the nut 34 has an enlarged end portion serving as engaging means for a heat-shrink or other environmental sealing sleeve 37.
The triaxial contact assembly 35 comprises an outer member 38 which is internally screw-threaded at its left-hand end for cooperation with an inner body nut 39 identical to and serving the same function as the inner body nut 7 of the plug, the outer member 38 being closely received within the bore of the receptacle body 30 with an external shoulder of the member 38 abutting against an internal abutment formed within the bore of the receptacle body 30. Within the outer member 38 of the triaxial contact assembly 35 and retained therein by the inner body nut 39 there is provided a coaxial contact assembly consisting of a male contact pin 40 having a cranked rear end integrally formed with a crimp bucket 41 for terminating one of the conductors of a single twisted pair screened cable 5, an electrically insulating mounting bushing 42 for the pin 40, a female contact 43 formed at its front end with a skirt comprised of a plurality of spring fingers which are sprung inwardly towards the receptacle axis at their tips and at its rear end with an integral crimp bucket 44 for terminating the other conductor of the cable 5, an electrically insulating tubular bushing 45 mounting the female contact 43 within the outer member 38 of the triaxial contact assembly, and an electrically insulating bushing 46 encompassing the crimp buckets 41 and 44 and serving inter alia for transferring the screw force of the inner body nut 39 to the insulating bushing 45 for securing an external shoulder formed thereon in abutting relationship with an internal shoulder formed within the bore of the outer member 38 of the triaxial contact assembly 35. A crimp sleeve 47 serves to secure the cable screen to the inner body nut 39.
Other features of the receptacle of Figures 2A and 2B will be apparent to the skilled reader from consideration of the detail shown in Figures 2A and 2B and will not be particularly described herein. It is however to be noted that the externally screw-threaded front (right-hand) end portion of the receptacle, similarly to the corresponding nose portion of the plug, is extended so as to protect the triaxial contact assembly against scoop or probe damage and also so as to ensure that as the receptacle mates with a plug as hereinbefore described the respective triaxial contact assemblies of the plug and of the receptacle necessarily approach and engage with each other coaxially. The complementary orientation keys and keyways respectively provided on the plug and on the receptacle ensure furthermore that a respective plug can be mated only with a receptacle having appropriate complementary keyways thereby protecting against incorrect assembly of a plug with the wrong one of a plurality of receptacles, and also provide for a rotation free mating of the plug and receptacle which minimises contact wear. The use of fine vee-threads in the screw-threaded parts of the plug and receptacle, and the locking action (hereinbefore described) of the O-ring seal 22 provided between the plug body 1 and its coupling ring 2 as the plug and receptacle are brought into fully mated condition by rotation of the coupling ring 2, ensures that the connectors are vibration proof in their fully mated condition.
As will be appreciated by those possessed of the appropriate skills and knowledge, the described and illustrated plug and receptacle provide advantageous features for the connection of single twisted pair screened cable as used for example in data highway systems particularly for military applications as in aircraft and tanks for example. The termination of the cable conductors by means of compression jointing techniques at coaxial contact assemblies incorporating integral crimp buckets, and the termination by a similar technique of the cable screen at the inner body nut which engages with a member which contains and encloses the coaxial contact assemblies and forms a triaxial contact assembly therewith, is fully compliant with accepted military standards and is sure and simple in use. The keyed outer body shells of the connectors are constructed to facilitate and ensure correct mating of respective connectors and provide scoop-proof and probe damage protection of the triaxial contact assemblies of the connectors, and the overall design of the connectors will be seen to be such as to ensure maximum protection of the contact assemblies both in the mated and the unmated conditions of the connectors. The outer body shells of the connectors furthermore ensure a high level of electrical screen continuity when the connectors are in their fully mated condition where the end surface of the plug male portion abuts the inner end surface of the female portion of the receptacle at a position where the outer contact members of the plug and receptacle triaxial contact assemblies make full and overlapping contact with each other. The mechanical integrity of the connectors is finally assured by the environmental sealing which is provided and by the 0-ring locking technique which is employed for retaining the coupling ring on the plug in its screwed-up condition when the plug and receptacle are fully mated.
The described and illustrated plug and receptacle are exemplary of the invention and it will be appreciated by those skilled in the art that various alterations and modifications could be made thereto. For example, whilst the described combination of male and female contact members in the plug and receptacle is presently preferred, variations could be made up to the extent of providing all male contact members on one connector and all female contact members on the other. The described connectors could also be modified for use with double braided cables as are sometimes used to improve overall screening in applications involving faster data transmission rates, an insulator being provided between the triaxial contact assembly and the outer body shell of the respective connector, and a second crimp termination being provided for accommodating the additional braid and contacting the outer body shell thus insulated from the triaxial contact assembly; the resultant arrangement of mated connectors would comprise two discrete screen continuity paths, namely a first path via the outer body shells of the connectors and a second path via the mated triaxial contact assemblies of the connectors.
As aforementioned, the invention also extends to adaptors which might comprise double-sided triaxial contact assemblies of the types described in the foregoing suitably retained within an outer plug or receptacle type body. Thus for example, a receptacle type adaptor might generally comprise the portion of the receptacle of Figure 2A to the right-hand side of the flange 31 integral with a mirror image thereof generally with respect to the plane of the flange 31.
Figure 3 of the accompanying drawings is a half axial sectional view of an exemplary adaptor designed to be utilized with plug type connectors as hereinbefore described with reference to Figure 1A. As shown, the adaptor comprises an outer body shell 50 which is externally screw-threaded at each end for cooperation with the coupling ring 2 provided on the plug type connector of Figure 1A, the outer body shell 50 being internally configured and dimensioned at its screw-threaded ends generally identically to the corresponding part of the receptacle type connector of Figure 2A. A flange 51 defining a recess for a sealing ring 52 is provided on the outer body shell 50 for enabling the adaptor to be panel mounted, a locking nut 53 completing the securement of the adaptor to the respective panel.
Within the outer body shell 50 of the adaptor, there is mounted a double-ended triaxial contact assembly 54 designed so as to present to a mating plug type connector a configuration at each end identical to that presented by the receptacle type connector of Figure 2A. The double-ended triaxial contact assembly comprises a double-ended axial male contact 55, a double-ended female contact 56 coaxial with the male contact 55 and electrically insulated therefrom by means of bushes 57 and 58, and a further double-ended male contact 59 coaxial with the male and female contacts 55,56 and electrically insulated from the female contact 56 by means of bushes 60 and 61. The thus formed triaxial contact assembly 54 is retained within the bore of the outer body shell 50 by means of a spring retaining clip 62 and bushes 63 and 64, which can be electrically conductive or electrically insulating depending upon whether or not the outer body shell 50 is desired to be electrically commoned with the male contact 59, are interposed between the outer body shell 50 and the male contact 59. Environmental sealing can be provided, if desired, by provision of elastomer seals 65.
In assembly of the adaptor of Figure 3, the bush 61 is first inserted into the right-hand side of male contact 59 (which, note, is formed in two parts which are secured together to complete the assembly of the double-ended triaxial contact assembly 54), then the right-hand end of female contact 56 is inserted into the bush 61, the bush 58 is then inserted and then the male contact 55 is inserted. Next the bush 57 is inserted past the clip 66 which is formed integrally with the female contact 56 and is retained in place by the clip 66, and then the bush 60 and the left-hand side of male contact 59 are introduced. The two sides of the male contact 59 are then secured together by turning over the edge 67 to complete the assembly 54 which is then inserted into the body shell 50 with the bushes 63 and 64 and secured therein by means of clip 62.
The plug and/or receptacle as hereinbefore described could furthermore be configured as a termination or dummy load in which case the single twisted pair screened cable shown in the drawings would be substituted by a resistor for example having its leads crimped to the crimp buckets of the respective connector. The outer body nut, in such an application, might be formed with a blind end rather than with a cable-receiving bore.

Claims

1. An electrical connector including a contact assembly (4;35) comprising first, second and third coaxial contacts (8,9,6;40,43,38) wherein the first contact (8;40) is coaxially embraced by and electrically insulated from the second contact (9;43) and the second contact (9;43) is coaxially embraced by and electrically insulated from the third contact (6;38), the contact assembly (4;35) being accessible at one axial end thereof for mating with a complementary connector, the first and second contacts (8,9;40,43) having conductor fastening means (11,14;41,44) provided integrally therewith at the opposite axial ends thereof for electrical and mechanical connection to the conductors of a single twisted pair screened cable (5), and means (7;39) being provided associated with the third contact (6;38) for electrical connection thereto of the screen of the single twisted pair screened cable (5).

2. An electrical connector according to claim 1 wherein said conductor fastening means (11,14;41,44) provided integrally with the first and second contacts (8,9;40,43) comprise crimp buckets adapted to receive therein the bared ends of the conductors of the single twisted pair screened cable (5) and to be crimped so as to mechanically deform into mechanical and electrical connection to the said conductors, the said crimp buckets being offset with respect to the axis of the connector.

3. An electrical connector according to claim 1 or 2 wherein the contact assembly (4;35) comprised of the first, second and third coaxial contacts (8,9,6; 40,43,38) is arranged such that the first and second contacts (8,9;40,43), together with associated electrically insulating bushes (10,12;42,45) for insulating the first and second contacts (8,9;40,43) from each other and for insulating the second contact (9;43) from the third contact (6;38), are captured within the internal void of the third contact (6;38) by means of a fastening means (7;39) adapted to be releasably secured to one end of the third contact (6;38), namely the end opposite to the end thereof which is accessible for mating with a complementary connector.

4. An electrical connector according to claim 3 wherein the said fastening means (7;39) for capturing the first and second contacts (8,9;40,43) within the internal void of the third contact (6;38) comprises a screw-threaded fastener (7;39) having screw threads adapted for engagement with complementary screw threads provided on the respective end of the third contact (6;38), and the said screw-threaded fastener is provided with abutment means serving, through the intermediacy of an electrically insulating bushing (15;46), to urge the first and second contacts (8,9;40,43) and their associated insulating bushes (10,12;42,45) into operative positional relationship with each other and with the third contact (6;38).

5. An electrical connector according to claim 3 or 4 wherein the said fastening means (7;39) for capturing the first and second contacts (8,9;40,43) within the internal void of the third contact (6;38) is further provided with said means for electrical connection to the third contact of the screen of a single twisted pair screened cable (5).

6. An electrical connector according to claim 5 wherein the said means for electrically connecting the screen of a single twisted pair screened cable (5) to the respective fastening means (7;39) comprises a tubular rearward projection for cooperation with a crimp sleeve (16;47) to enable the requisite connection to be made.

7. An electrical connector according to any of the preceding claims wherein the contact assembly (4;35) comprised of the first, second and third contacts is housed within an outer body shell (1,3; 30,34) which is adapted to mate with the complimentary outer body shell of a complimentary connector.

8. An electrical connector according to claim 7 wherein the outer body shell (1,3;30,34) of the connector is provided with formations (20;33) to ensure that the connector can be mated only with a complementary connector having complementary formations.

9. An electrical connector according to claim 7 or 8 wherein the contacts (8,9,6;40,43,38) of the connector are recessed within the outer body shell (1,3;30,34).

10. An electrical connector according to claim 7 or 8 or 9 wherein the outer body shell (1,3;30,34) of the connector is formed of an electrically conductive material to provide radio-frequency screening and is adapted to be made electrically continuous with the screen of a screened cable (5).

11. An electrical connector according to any of claims 7 to 10 which is adapted for use with a double screened cable by virtue of the outer body shell of the connector being electrically insulated from the third contact and provision being made for connection of the outer screen of the cable to the outer body shell.

12. An electrical connector according to any of claims 7 to 11 wherein the outer body shell (1,3) of the connector comprises a male portion (19) adapted to mate with a female portion (32) of the outer body shell (30,34) of a complementary connector and an internally screw-threaded coupling ring (2) is affixed to the connector for cooperation with external screw threads provided on the said female portion (32) for retaining the two connectors in mating engagement, and an elastomeric 0-ring (22) is captive within a recess defined between the coupling ring (2) and the body shell (1) of the connector, the arrangement being such that when the connector is in mated engagement with a complementary connector the 0-ring (22) is subjected to axially compressive forces causing it to expand its radial dimension thereby frictionally locking the coupling ring (2).

13. An electrical connector according to any of the preceding claims wherein the second contact (9;43) is of the opposite sex (i.e. male or female) to the first and third contacts (8,6;40,38).

14. An electrical connector according to any of the preceding claims wherein the said conductor fastening means (11,14;41,44) provided integrally with the first and second contacts (8,9;40,43) are adapted for connection to conductors cut to the same length.

15. An electrical connector according to any of the preceding claims in mating relationship with a complementary connector or with an adaptor.