US3199061A

US3199061A - Coaxial connector

Info

Publication number: US3199061A
Application number: US255235A
Authority: US
Inventors: Ernest H Johnson; William E Voigt
Original assignee: Andrew LLC
Current assignee: Commscope Technologies LLC
Priority date: 1963-01-31
Filing date: 1963-01-31
Publication date: 1965-08-03
Anticipated expiration: 1982-08-03

Description

3, 1955 E. H. JOHNSON ETAL 3,199,061

COAXIAL CONNECTOR Filed Jan. 31, 1963 INVENTORS United States Patent 3,19,061 CGAXIAL (IGNNEQTQR Ernest H. Johnson, Chicago, and William E. Voigt, Thornton, llh, assignors to Andrew Corporation, Uri-and Park, lit, a corporation of Illinois Filed Jan. 31, 1963, 821'. No. 255,235 19 Qlairns. (til. 339-1tbtl) This invention relates to coaxial connectors, and more specifically to coaxial connectors of the type for use at high frequencies with high-power low-loss types of coaxial cables having relatively large center conductors.

The principal object of the invention is the provision of connectors having an inner conductor construction permitting simple and secure attachment to the center conductor of the cable to which the connector is attached as a termination or coupling. Such high-power cables normally employ, because the current flow is cylindrical due to skin effect, fairly thick-walled hollow tubular center conductors. Normally, a solder joint has been heretofore made between the center conductor of the connector and the center conductor of the cable, but various types of solderless connections have been employed in order to simplify assembly of the connector to the cable, particularly in the field. Solderless connections of the types heretofore employed, however, have been in general subject either to the objection of complexity of mechanical assembly operations, or that of unreliability of electrical performance after installation. In the assembled device, it is extremely important that joints not merely have low resistance as measured on a direct-current meter, as is in general satisfactory at low frequencies, but also that the current path be maintained without substantial discontinuity in the outer circumferential portion. Any discontinuity in conductivity in this outer portion reflects itself, at the high frequencies at which these cables are used, as an impedance discontinuity and source of loss in the cable, even though the outer discontinuity is bridged by an inner current path which presents as much or more cross-sectional area of conductor than the outer tubular portion, and thus demonstrates, at direct current or low frequencies, a lower resistance than the tubular skin conductor itself, since at the high frequencies it is only this skin which is effective. One construction of connector center conductor in common use employs a conductor having a body portion of the same diameter as the outer diameter of the tube, with a lead or extension portion of an outer diameter equal to the inner diameter of the tube, so that the lead extension fits securely into the tube, the shoulder at the end of the body portion seating the end of the tubular conductor of the cable. Conventionally, such a construction is soldered in place, care being taken to assure that the solder (normally a braze) makes an unbroken longitudinal interface between the shoulder on the connector conductor and the end of the tubular cable conductor.

As in the case of other types of connectors, it has long been known that it is desirable to eliminate the soldering or brazing operation in such an assembly, particularly if assembly is to be made in the field, Where facilities for making such a brazed or soldered joint are frequently unavailable, and at best inconvenient to obtain.

Generally similar problems in connection of the outer conductors of the cable and the connector, respectively, have long since found satisfactory solutions. But as regards the center conductor, the provision of a fully satisfactory joint without the employment of a soldering or brazing operation has heretofore been lacking.

The present invention, not only meeting the need described above, but meeting it in a manner introducing 3,199,061 Patented Aug. 3, 1965 no substantial complexity in manufacture, will best be understood from a description of particular embodiments thereof as illustrated in the drawing, from which the broader teachings of the invention, and the manner of their application to permit adaptation of the invention to many types of embodiments other than those illustrated, will be obvious.

in the drawing:

FIGURE 1 is a longitudinal sectional view of a coaxial connector made in accordance with the invention;

FIGURE 2 is a transverse sectional view of the connector taken along the line 2-2 of FIGURE 1 in the direction indicated by arrows;

FIGURE 3 is an enlarged end view of the termination or attachment portion of the center conductor of the connector;

FIGURE 4 is a side elevational view of a connector center conductor constituting an alternate form of that shown in the figures previously described, illustrating in section the insulator in which the conductor is mounted;

FIGURE 5 is a transverse sectional view taken along the line 55 of FIGURE 4 in the direction indicated by arrows;

FIGURE 6 is an enlarged sectional view showing the connector conductor of FIGURE 4 assembled with the tubular center conductor of a coaxial cable, certain features being somewhat exaggerated for clarity of illustration;

FIGURE 7 is a view more or less similar to that of FIGURE 4, but illustrating a further modified construction of the center conductor; and

FIGURE 8 is a transverse sectional view taken along the line 8--S of FIGURE 7 in the direction indicated by arrows.

For convenience of reference, in the description and in the claims hereto appended, the forward end of a connector will be considered as the end normally con structed for engagement with a mating connector, and the rearward end Will be considered as the end to which the cable is joined.

The connector illustrated in FIGURES 1 through 3 consists generally of an outer conductor assembly 10 within which is mounted an insulator 12, which in turn supports an axial inner conductor 14.

The outer conductor assembly has a body or shell 16 which is rotationally mounted in a flange 18 provided with bolts and nuts 20 for connection to a similar flange (shown dotted in schematic form) or to a panel, etc., for through connection of the cable. The rotatable mounting is formed by a snap ring 22 mounted in suitable mating channels in the body 16 and the flange 18, respectively. As will be obvious, the particular type of coupling or joint for which the connector is designed (flange, threaded-coupler, etc.) is of no relevance to the invention, the center conductor construction to be described being usable not only with any type of mating coupling, of which there are many, but also with outer conductor constructions of a large variety of kinds of details. In the particular embodiment illustrated the shell or body 16 is provided with a threaded plug 24 for gas-filling, etc., in the manner well known in the art. in its rearward portion, the shell or body 16 is internally threaded at 26 and cooperates with an externally th eaded clamping nut or ferrule 28 to clamp the end of the outer conductor of the cable (not shown) between an internal conical bevel 30 on the nut or ferrule 28 and a cooperating external conical bevel on the rearward surface of a clamping ring 32, the forward surface of which seats on 'a shoulder formed on the interiorof the body 16 of the outer conductor portion of the connector. An appropriately formed rubber gasket 36 is d: seated within an internal shoulder on the nut or ferrule 28. Within the outer or rearward end of the nut 28 is a support band or ring 38, held in place by a retaining ring seated in an appropriate groove. The interface between the body 16 and the nut 23 is gas-sealed by an O ring 42.

The parts as thus far described constitute merely one type of outer conductor connector construction with which the inner conductor improvement of the present invention may be employed, and therefore need not be described in detail herein either in construction or function. It may merely be observed that with the construction described, attachment of the outer conductor of the cable to the connector may be made by tightening of the nut with respect to the body, thus tightly clamping the end of the outer conductor between the two portions of the outer conductor assembly of the connector described above, and providing a firm electrical connection without introduction of any substantial alteration of outer conductor inner diameter. It will be observed that as shown in the drawing, the internal portions are formed to receive an outer conductor of the helically corrugated type, but it will also be later observed that the present invention is not necessarily limited to this type of construction.

The longitudinally central portion 44 of the center conductor 14 is of reduced diameter as compared with the portions extending in each direction from it, which are of substantially the same diameter as the outer diameter of the conductor to which the center conductor of the connector is to be joined.

It will of course be understood that the forward portion 46 of the inner conductor 14 may take any of a variety of shapes and forms, depending upon the construction of the connector, cable, or other device, to which it is designed to be connected, this feature of construction, i.e., configuration of the forward portion of the center conductor, and the manner of its connection to a further center conductor being irrelevant to the present invention, and the solid cylindrical form of the portion 46 as illustrated in the drawing accordingly being more or less schematic, one form of termination at this end employing a hollowed-out cylinder designed to receive a properly fabricated lead or guide portion of another connector. The length of the central portion 44 of reduced diameter just mentioned is substantially the same as the thickness of the insulator 12, so that the center conductor is firmly seated in the insulator, between the rearward end of the enlarged forward portion 46 and a shoulder surface 48 on the center conductor portion just rearward of the portion 44 of small diameter, this latter shoulder 48 being again of the same diameter as that of the tube forming the center conductor of the cable for which the connector is designed. Rearward of the shoulder portion just described is a conically tapered portion (i.e., tapered to smaller diameter if considered as extending rearwardly, but flared to larger diameter if considered as extending forwardly). The large or forward end of the flare or taper 50 is of somewhat smaller diameter than the shoulder 48, there being a small shoulder 52 at the forward end of the taper or flare 50. Rearward of the flare or taper 50, the termination portion, which is of smaller diameter than the tubular conductor of the cable for which the connector is designed, is externally threaded with a suitable coarse thread 54 and ends in a tapered or reduced lead portion 56. In the rearward portion of this termination, a thread-cutting edge is formed by the cutting away at 58 of a portion of the originally circular body. As illustrated, the threadcutting edge is formed by a milling tool or circular saw cutting away about 90 degrees of the generally circular configuration near the end, the cut of course diminishing in depth with increased distance from the end, as is conventional in similar types of formation of self-tapping screws by interruption of the threads to form a threadcutting edge. Obviously, although this simple type of formation of the thread-cutting edge is highly advantageous, as regards cost and simplicity, many other types of self-tapping screw terminations may be employed.

The central portion 44 has a diametric aperture 60. This aperture may be used for the engagement of a simple tool like a large nail or a steel rod to permit installation of the center conductor of the connector in the center conductor of the cable, a configuration of complete circular symmetry providing no simple manner of grasping the conductor to apply the torque necessary for such installation. The manner of assembly will be further discussed hereinafter, but for present purposes it may merely be noted that the insulator is split, being formed of two pieces as shown at 62, and is furthermore provided with apertures 64 for the purpose of gas communication, the sizes of these apertures being selected to provide appropriate impedance continuity in the region of the insulator. In the present instance, the compensation for the deviation from circular symmetry may readily be accomplished by suitable alteration of the normal insulator compensation, the dimensioning 0f the inner and outer conductors in this region compensating for the difference in dielectric constant of the insulator from that of the adjacent gas-filled regions, which are of course of lower dielectric constant, the apertures also, of course, entering into the preservation of the desired continuity of characteristic impedance.

In FIGURE 4 is shown a somewhat different, although generally similar, embodiment of the invention. Here the inner conductor 14a has a central portion 44a generally similar to the central portion 44 previously described, but of completely circular symmetry. The forward portion 46a is the same as described in connection with the p vious embodiment, as is the conical flare or taper 59 terminating at its forward end at the shoulder 52a and externally threaded at 54a with the cut-away 58a formin the thread-cutting portion. There are, however, certain differences from the previous embodiment. Here, there is provided an elongated unthreaded lead portion 66 which has been found to simplify the task of starting the threading with assurance that it is circularly symmetrical and straight into the end of the tube, without the necessity of care to assure that the threading is commenced with the screw exactly coaxial with the copper tube conductor. A second diiference lies in the provision for application of torque by a suitable tool. As previously indicated, in this embodiment there is no aperture within the insulator as in the previous embodiment. Here, there is provided instead a pair of parallel flats 68 formed on the region of the conductor immediately adjacent to the rear surface of the insulator, i.e., to the portion 44a, this pair of flats serving for grasping by a wrench or similar tool. Although the variation from circular symmetry here used to permit the application of torque is not directly in th insulator, it is found that by making it directly adjacent to the insulator, with its longitudinal extension substantially shorter than the thickness of the insulator, any characteristic impedance change caused by the deviation may readily be corrected in the insulator without further provision.

In FIGURE 6 is shown, with certain of the features of construction more or less exaggerated for clarity, the center conductor 14a of FIGURES 4 and 5 as installed in the end of a tubular center conductor 70 of a coaxial cable. This view illustrates the manner in which the present invention assures the contact in the peripheral region of the joint which is of the essence of the requirement for successful high-frequency use of a coaxial connector. As shown in this view, when the screw connection is tightened in the threads formed by the thread-cutting edge on the inner surface of the tube 70, the end of the tube strikes the flare 50a. at its inner diameter, and the further tightening of the screw to the point where the end of the tube ultimately strikes the shoulder 52a, constituting the end-stop, the tube being slightly flared or forced-fitted over the slight flare in the terminal portion of the tightening, thus assures a fairly large-area tight and secure contact in the region of the forward portion, or largest portion, of the flare 50a, which is immediately adjacent to the largest diameter port-ion of the central conductor of the connector (corresponding to the outer diameter of the undistorted tube), so that there is no substantial alteration of the radial distance from the axis having a secure conductive path. The cooper, being soft, tends to deform into tight engagement of its end surface with the shoulder 52a. However, since it is desirable that the installation be made without the necessity of preparing the end of th tube in any manner, after the end of the cable has been cut off with an ordinary cutting tool such as a hack-saw, for example, it is not desirable to rely solely on the interface between the end of the tube 79 and the shoulder 52o (i.e., on the joint which would be formed if the taper at Sta were omitted). The taper Silo assures that the proper contact will be made on approximately the proper radius and over a large enough area so that no substantial discontinuity of the effective diameter of the overall conductor is introduced. It may be noted in this regard that even though the threads 54a may themselves be in secure electrical contact with the tube '75, the formation of a skin of the same thickness as that of the tube within the threaded portion of the inner connector conductor would produce a current path of substantial length of greatly reduced diameter. It should be observed that the drawing of FIGURE 6 somewhat exaggerates certain of the features of construction for purposes of clarity of illustration. In practice, the total flare or taper of the part Silo produces an expansion or flaring of the end of the tube 7:) which is barely perceptible, being just sufficient to assure the desired seating and circumferential contact, the expansion commencing only in a very small region prior to the striking of the shoulder 52a. by the end of the tube. This is rather readily controlled with very small tolerance by reason of the fact that the tube 7% is normally of precision manufacture, with well-controlled thickness and diameter, so that the conductor of the coaxial connector, fabricated with similar precision, and centered in installation by the long lead portion 66, can be made to permit highly precise control of the exact stopping point and degree of flaring of the tube Without the exercise of anything but a minimum care on the part of the operator, practically the sole requirement of car lying in the fairly conventional operation of assuring that the cut-off of the end of the cable is reasonably square.

As previously indicated, certain of the features are somewhat exaggerated in FIGURE 6 to permit rea y visualization of the manner in which the benefits are .achieved. Actually, in practice, the maximum or forward diameter of the flare Sila (or of the flare Ed) is approximately equal to the crest or maximum diameter of the threads, or enough greater than the root diameter of the threads to produce sufiicient force fit on the inner portion of the conical surface to assure secure contact, while producing negligible outer diameter variation in the continuous inner conductor thus formed. The angle of the cone is preferably very small in order to assure that great force will not be required in the tightening operation to procure the desired type contact. On the other hand, of course, it is not desirable to make the cone so gradual in inclination that an excessive number of turns is required for tightening. An angle of between 5 degrees and degrees with respect to the axis is found to produce the most desirable results, with a 10 degree angle being most suitable for most tubular conductor sizes in use on coaxial cables.

In EEGURES 7 and 8 is shown a further variant. lere, the inner conductor 1412 has a central portion 441), a forward portion 461'), a conical flare 5 311, a shoulder 5212, an externally threaded portion 54b, and a cut-away 58b forming a thread-cutting edged, generally corresponding to the structure shown in FIGURE 1. However, in this instance, the deviation from circular symmetry which forms the gripping point for the application of torque is provided by parallel lists 72 on the central portion 44b which is surrounded by the insulator 12. It will thus be seen that in essence the embodiment of FIGURES 7 and 8 may be said to incorporate the type of tool grip shown in the embodiment of FIGURE 4, but in the configuration of FIGURE 1, in which the tool grip portion is directly within the insulator, rather than immediately adjacent as in FIGURE 4.

Many other variants will be obvious from the embodiments illustrated in the drawing an described above. Further, it will be found upon study that although all three of the embodiments illustrated are closely similar, and incorporate the same overall general combination of fea tures, certain of the features may readily be adapted to constructions in which other elements of the combination are not necessarily present. Thus it will be seen, for example, that the novel manner of providing peripheral contact between the central conductor of the connector and the central conductor of the cable may be utilized by the provision of the conical or tapered flare of the connector conductor even in cases where the manner to tightening this forced fit is somewhat different, although the combination of the self-tapping screw arrangement with the conical flare offers great advantage in the simplicity of construction and assembly in simultaneously making the mechanical anl electrical connection with the desired security.

The overall manner of assembly will of course be obvious to those skilled in the art. It will be seen that the shoulder 52. which marks the stop for the end of the inner conductor of the cable is substantially in the same transverse plane as the outer or forward end of the clamp formed by the bevel 3t and the clamping ring 32. Thus a square cutoff of the inner and outer conductors is substantially all the preparation of the cable-end required. The center conductor 14 (or 14a or 141)) is threaded into the center conductor of the cable, the split ring insulator is placed around the small-diameter central portion 44 (the splitting of the ring preferably having a small unitary hinge portion, in the manner well known in the art), the nut or ferrule 28 is placed on the outer conductor of the cable (in more or less threaded engagement in the present helically corrugated configuration), the end of the cable is inserted into the body, thus seating the insulator 12. on the shoulder 34, the ring 32 is seated on the rear- Ward side of the insulator (having been inserted in the annulus between the inner and outer conductors before putting on the insulator), and the nut or ferrule 28 is then tightened to clamp the outer conductor and complete the assembly.

As previously indicated, many variants of the construction illustrated and described will readily be devised by persons skilled in the art after study of the basic teachings of the invention. Accordingly, the scope of the invention should not be limited by the particular embodiments herein shown, but shall be determined in accordance with t e constructions as described in the claims hereto appended, and equivalents thereof.

What is claimed is:

1. A high-frequency connector comprising:

(a) an outer shell having therein a tubular outer conductor connector portion and means for clampingly securing said tubular portion to the end portion of a cable outer conductor of substantially the same inner dimension as said tubular portion to form an outer conductor joint of substantially continuous innor dimension,

(b) at least one annular insulator within the shell, and

(c) a center conductor supported by the insulator,

(d) the rearward portion of the center conductor having thereon an exterior threaded termination for screw-in attachment to the corresponding conductor of a cable, and

(e) a conical flare, of maximum diameter exceeding the root diameter of the threads on the termination, by an amount small compared to the crest diameter of the threads on the termination, at the inner end of the termination, so that tightening of the screw-in connection produces a force fit of the leading portion of the cable conductor on the conical flare to establish firm contact around the entire circumference and form an inner conductor joint of substantially continuous outer dimension.

2. The connector of claim 1 wherein the threaded termination includes a thread-cutting end.

3. The connector of claim 2 wherein the thread-cutting end comprises a threaded portion having an uninterrupted thread.

4. The connector of claim 2 wherein the thread-cutting end terminates in an unthreaded portion or" substantially the root diameter of the thread.

5. The connector of claim 1 wherein the taper of the flare portion is between 5 degrees and degrees.

6. The connector of claim 1 having, at the forward end of the flared portion, a rearwardly facing shoulder adapted to receive the leading end of the cable conductor to limit the tightening of the threaded connection, the shoulder being of liameter adapted substantially to match that of the cable conductor.

7. The connector of claim 6 having on the internal surface of the shell a rearwardly facing internal shoulder substantially in the transverse plane of the shoulder on the inner conductor, so that the ends of the respective conductors of a transversely cut-oft cable substantially seat on the respective shoulders upon completion of assembly.

8. The connector of claim fl having, between the flared portion and forward portion, a short tool-engaging portion deviating from circular symmetry.

9. The connector of claim 8 wherein the tool-engaging portion comprises flat exterior surfaces.

10. The connector of claim 8 wherein the tool-engaging portion comprises a diametric aperture.

11. The connector of claim 8 wherein the tool-engaging portion is substantially in the longitudinal region of support of the center conductor by the insulator.

12. The connector of claim 11 wherein the insulator surrounds the tool-engaging portion.

13. The connector of claim 11 wherein the tool-engaging portion abuts against one face of the insulator and is of greater transverse dimension than the portion surrounded by the insulator.

14. A high-frequency coaxial connector comprising:

(a) an outer shell having therein a tubular outer conductor connector portion and means for clarnpingly securing said tubular portion to the end portion of a cable outer conductor of substantially the same inner dimension as said tubular portion to form an outer conductor joint of substantially continuous inner dimension,

(b) at least one annular insulator within the shell, and

(c) a center conductor supported by the insulator,

(d) the rearward portion of the center conductor being an elongated externally threaded solid termination adapted to threadedly engage the end of a hollow corresponding conductor of a cable, and

(e) a conical flare, of maximum diameter exceeding the root diameter of the threads on the termination, at the inner end of the termination, so that the leading portion by an amount small compared to the crest diameter of the threads on the termination, of such conductor of the cable may be forced onto the conical flare by tightening of the threaded engagement to establish firm contact around the entire circumference and form an inner conductor joint of substantially continuous outer dimension. 15. The connector of claim 14 wherein the taper of the flare is between 5 degrees and 15 degrees.

16. The connector of claim 14 having, at the forward end of the flare, a rearwardly facing shoulder adapted to receive the leading end of a cable conductor to limit the a forcing thereof onto the flare.

1'7. A high-frequency coaxial connector comprising:

(a) an outer shell having therein a tubular outer conductor connector portion and means for clampingly securing said tubular portion to the end portion of a cable outer conductor of substantially the same inner dimension as said tubular portion to form an outer conductor joint of substantially continuous inner dimension,

(b) at least one annular insulator within the shell, and

(c) a center conductor supported by the insulator,

(d) the rearward portion of the center conductor having theron an exterior threaded termination for screwin attachment to the corresponding conductor of a cable and (e) a rearwardly facing shoulder adapted to be engaged by the leading end of the cable conductor to limit the tightening of the threaded engagement, and a flare tapered at an angle of at most approximately 15 degrees connecting said rearward portion and said shoulder, and

(f) a short tool-engaging portion deviating from circular symmetry forward of the threaded portion,

(g) so that the center conductor may be tightened into the cable conductor to force-fit the inner surface of the cable conductor over the flare.

13. The connector of claim 17 wherein the tool-engaging portion comprises flat outer surfaces formed on the conductor.

19. The connector of claim 17 wherein the tool-engaging portion abuts against the rearward face of the insulator and extends rearwardly to the shoulder.

References Cited by the Examiner UNITED STATES PATENTS 2,056,248 10/36 Buchanan 339268 2,156,272 5/39 Bell 339- X 2,451,868 10/48 Quackenbush et al. 339177 X 2,540,606 2/51 Beezley 339268 2,577,049 12/51 Uline 174-35 X 7,755,451 7/56 Smyers 399477 2,887,667 5/59 Wolfe et a1. 339177 X 2,967,289 1/61 Day 339268 3,109,691 11/63 Burkhardt 339-400 ALBERT H. KAMPE, Primary Examiner.

JOSEPH D. SEERS, W. DONALD MILLER, Examiners.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 5,199,061 August 3, 1965 Ernest H. Johnson et al.

It is hereby certified that error appears in the above numbered patent requiring correction and that. the said Letters Patent should read as corrected below.

Column 5, line 9, for "cooper" read copper line 74, for "edged" read edge column 6, line 23, for "to" read of line 28, for "anl" read and same column 6, line 62, after "high-frequency" insert coaxial column 7, line 25, for liameter" read diameter column 8, line 1, after "termination" insert by an amount small compared to the crest diameter of the threads on the termination lines 3 and 4, strike out "by an amount small compared to the crest diameter of the threads on the termination,"; same column 8, line 37, for "portion," read portion. line 38, beginning with "(g) so that the" strike out all to and including "over the flare." in line 40, same column 8.

Signed and sealed this 22nd day of February 1966.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents

Claims

1. A HIGH-FREQUENCY CONNECTOR COMPRISING: (A) AN OUTER SHELL HAVING THEREIN A TUBULAR OUTER CONDUCTOR CONNECTOR PORTION AND MEANS FOR CLAMPINGLY SECURING SAID TUBULAR PORTION TO THE END PORTION OF A CABLE OUTER CONDUCTOR OF SUBSTANTIALLY THE SAME INNER DIMENSION AS SAID TUBULAR PORTION TO FORM AN OUTER CONDUCTOR JOINT OF SUBSTANTIALLY CONTINUOUS INNER DIMENSION, (B) AT LEAST ONE ANNULAR INSULATOR WITHIN THE SHELL, AND (C) A CENTER CONDUCTOR SUPPORTED BY THE INSULATOR, (D) THE REARWARD PORTION OF THE CENTER CONDUCTOR HAVING THEREON AN EXTERIOR THREADED TERMINATION FOR SCREW-IN ATTACHMENT TO THE CORRESPONDING CONDUCTOR OF A CABLE, AND (E) A CONICAL FLARE, A MAXIMUM DIAMETER EXCEEDING THE ROOT DIAMETER OF THE THREADS ON THE TERMINATION, BY AN AMOUNT SMALL COMPARED TO THE CREST DIAMETER OF THE THREADS ON THE TERMINATION, AT THE INNER END OF THE TERMINATION, SO THAT TIGHTENING OF THE SCREW-IN CONNECTION PRODUCES A FORCE FIT OF THE LEADING PORTION OF THE CABLE CONDUCTOR ON THE CONICAL FLARE TO ESTABLISH FIRM CONTACT AROUND THE ENTIRE CIRCUMFERENCE AND FORM AN INNER CONDUCTOR JOINT OF SUBSTANTIALLY CONTINUOUS OUTER DIMENSION.