A length-adjustable power transmission line fitting

Abstract

This invention pertains to the field of power transmission lines, specifically a power transmission line length adjustment fitting, comprising: an adjusting sleeve having an axially penetrating non-circular cross-section inner hole; a left screw and a right screw, respectively inserted into the non-circular cross-section inner hole from both ends of the adjusting sleeve; each of the left and right screws is divided into three axially segmented sections: a non-circular cross-section rod section whose outer circumferential shape matches the shape of the non-circular cross-section inner hole of the adjusting sleeve; by locking the non-circular cross-section inner hole of the adjusting sleeve with the non-circular cross-section rod section of the screw, the torque transmission function and axial guiding function of the fitting are decoupled. The adjusting sleeve only transmits torque and does not bear thread guidance, eliminating relative torsion between the adjusting sleeve and the screw from a kinematic perspective, thus solving the problem of torsional loosening caused by the accumulation of micro-motion in the thread pair clearance under alternating loads such as wind vibration and temperature changes in traditional helical length adjustment fittings.

Description

Technical Field

[0001] This invention relates to the field of power transmission lines, specifically a power transmission line length adjustment fitting. Background Technology

[0002] In power transmission lines, the connection between insulator strings and towers / conductors is achieved through fittings. Among these, length adjustment fittings are used to precisely adjust the length of insulator strings and conductor sag, and are key components to ensure the safe operation of the line. Currently, the length adjustment fittings widely used in the power industry are mainly of a spiral structure, with a typical example being the turnbuckle (also known as a rigging screw or tensioning screw).

[0003] The basic structure of a traditional spiral length adjustment fitting includes: an intermediate adjusting sleeve (or adjusting rod) with left-hand and right-hand internal threads machined on the inner walls of its two ends, respectively; two end pull rods (or screws) with corresponding external threads, screwed into the ends of the adjusting sleeve; and a connecting ring or connecting fork located at the end of the pull rod. In use, rotating the intermediate adjusting sleeve with a wrench causes the pull rods to screw in or out simultaneously, thus achieving stepless adjustment of the overall length of the fitting. In the actual operating environment of transmission lines, after the length adjustment fitting is installed, adjusted, and under load, under the long-term action of complex alternating loads such as wind-induced vibration, conductor micro-wind vibration, electromagnetic force alternation, and environmental temperature cycling, the threaded pair between the adjusting sleeve and the pull rod will experience minute circumferential relative rotation. This micro-movement accumulates over time, eventually leading to loosening of the threaded connection and unexpected elongation or shortening of the fitting length, seriously affecting the sag accuracy and operational safety of the line. Existing solutions mainly include adding locking nuts at both ends of the adjusting sleeve to eliminate thread clearance through double-nut counter-rotation; or using friction-increasing methods such as applying anti-loosening adhesive or using nylon inserts. However, these measures are all additive improvements on the original threaded pair and do not change the coupled nature of the threaded pair, which simultaneously undertakes the functions of torque transmission and guidance. In the harsh vibration environment of transmission lines, locking nuts may loosen due to fretting, ratchet mechanisms suffer from wear and increased clearance, and anti-loosening adhesives are at risk of aging and failure. More importantly, these additional structures increase the number of parts, assembly complexity, and manufacturing cost of the fittings, while the reliability of anti-loosening measures remains limited by the inherent defects of the single interface of the threaded pair. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention proposes a power transmission line length adjustment fitting.

[0005] The technical solution adopted by this invention to solve its technical problem is: a transmission line length adjustment fitting as described in this invention, comprising: The adjusting sleeve has an axially continuous non-circular cross-section inner hole. The left and right screws are respectively inserted into the non-circular cross-section inner hole from both ends of the adjusting sleeve; The left and right screws are each divided into three sections along the axial direction: The outer circumferential shape of the non-circular cross-section rod section matches the shape of the non-circular cross-section inner hole of the adjusting sleeve. The two form an axial sliding fit with a circumferential shape lock, so that the adjusting sleeve can drive the left screw and the right screw to rotate synchronously, while allowing the two to slide relative to each other along the axial direction. The cylindrical external thread section, located at the end away from the adjusting sleeve, is used for threaded engagement with an external connector; The transition section is located between the non-circular cross-section rod section and the cylindrical external thread section; The adjusting sleeve transmits torque and restricts relative circumferential rotation only through the shape locking between the non-circular cross-section inner hole and the non-circular cross-section rod body section. The inner wall of the adjusting sleeve does not have a thread structure that mates with the cylindrical external thread section in the area corresponding to the non-circular cross-section rod body section of the left and right screws, thereby decoupling the torque transmission function and axial guiding function of the hardware and preventing torsional loosening caused by the thread pair clearance under alternating loads.

[0006] Furthermore, the non-circular cross-section inner hole is a regular hexagon, and the non-circular cross-section rod sections of the left and right screws are corresponding to regular hexagonal prisms.

[0007] Furthermore, the external connector includes an upper connecting platform and a lower connecting platform, both of which have upper threaded holes and lower threaded holes for the cylindrical external thread section to be screwed into. On the cylindrical external thread section of the left screw, from the adjusting sleeve toward the end of the left screw, an inner locking nut, the upper connecting platform, and an outer locking nut are sequentially fitted. On the cylindrical external thread section of the right screw, from the adjusting sleeve toward the end of the right screw, an inner locking nut, the lower connecting platform, and an outer locking nut are sequentially fitted. Both the inner and outer locking nuts are threadedly engaged with the corresponding cylindrical external thread section, and by tightening them in opposite directions, the upper or lower connecting platform is clamped and locked between the two to eliminate the thread gap of the cylindrical external thread section and lock the axial position.

[0008] Furthermore, the diameter of the transition section cylindrical smooth rod segment is larger than the major diameter of the cylindrical external thread segment, thereby forming an annular step surface between the non-circular cross-section rod segment and the cylindrical external thread segment; A butterfly spring is provided between the annular stepped surface and the end face of the adjusting sleeve; The disc spring is in a compressed state when assembled, and applies an axial preload to the adjusting sleeve to eliminate the axial clearance of the non-circular cross-section mating surface and suppress slight axial movement.

[0009] Furthermore, self-lubricating guide rings are embedded at the two openings of the non-circular cross-section inner hole of the adjusting sleeve; The inner cross-sectional shape of the self-lubricating guide ring is consistent with the shape of the non-circular cross-sectional inner hole, and its material is polytetrafluoroethylene composite material.

[0010] Furthermore, the thread pitch of the cylindrical external thread section of the left screw is P1, and the thread pitch of the cylindrical external thread section of the right screw is P2, and P1 is not equal to P2. With the left and right screws having unequal pitches, when the adjusting sleeve is subjected to external vibration and tends to rotate, the screws at both ends generate mutually restrictive reverse torques due to the difference in pitch, forming a differential interlocking effect.

[0011] Furthermore, the outer surfaces of both ends of the adjusting sleeve are machined with external threads, and locking rings are fitted onto the external threads; The locking ring has an internal thread and can be screwed in axially along the adjusting sleeve to press against the transition end face of the left or right screw, thereby achieving strong axial locking.

[0012] Furthermore, the sidewall of the locking ring and the sidewall of the adjusting sleeve are respectively provided with radial pin holes. A stop pin passes through the radial pin hole. The tail of the stop pin is provided with a radial small hole. A cotter pin passes through the radial small hole. The two metal wires of the cotter pin pass through the radial small hole and bend in opposite directions. The outer dimension of the bent wire is larger than the diameter of the radial through hole on the locking ring. The end of the bent metal wire abuts against the outer wall surface of the locking ring to prevent the stop pin from axially dislodging from the radial through hole.

[0013] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention decouples the torque transmission function and axial guiding function of the fitting by adjusting the shape of the non-circular cross-section inner hole of the sleeve and the non-circular cross-section rod body. The adjusting sleeve only transmits torque and does not undertake thread guidance. From a kinematic perspective, it eliminates the relative torsion between the adjusting sleeve and the screw, and solves the problem of torsion loosening caused by the accumulation of micro-motion in the thread pair clearance under alternating loads such as wind vibration and temperature changes in traditional spiral length adjustment fittings.

[0014] 2. This invention eliminates the thread fit clearance of the connecting table by setting internal and external locking nuts to clamp the connecting table on the external thread section of the screw cylinder; at the same time, a disc spring is set between the step surface of the transition section and the end face of the adjusting sleeve to apply axial preload, suppressing axial movement and fretting wear of the non-circular cross-section mating surface, and improving the overall length stability of the hardware.

[0015] 3. This invention reduces the frictional resistance of non-circular cross-section sliding fit by embedding self-lubricating guide rings at both ends of the inner hole of the adjusting sleeve, making the adjustment operation easier and smoother, while avoiding seizing and wear caused by direct metal contact, and extending the maintenance-free cycle.

[0016] 4. By adopting a differential thread design with unequal pitches on the left and right screws, when the adjusting sleeve is vibrated and tends to rotate, the two ends generate mutually restrictive reverse torques due to the difference in pitch, forming a differential interlocking effect, which further improves the reliability of anti-loosening.

[0017] 5. This invention adds a locking ring and a stop pin structure. The locking ring is screwed into the end face of the transition section of the clamping screw along the external thread of the sleeve to achieve axial strong locking. The stop pin prevents the locking ring from loosening, providing the highest level of anti-loosening protection for heavy-load or important crossing lines. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the overall structure of the present invention; Figure 2 For the present invention Figure 1 Enlarged structural diagram at point A in the middle; Figure 3 This is a cross-sectional structural diagram of the present invention; Figure 4 For the present invention Figure 3 Enlarged structural diagram at point B; Figure 5 This is a schematic diagram of the adjusting sleeve structure of the present invention; Figure 6 This is a schematic diagram of the connection structure between the lower connecting platform and the right screw of the present invention; Figure 7 This is a schematic diagram of the right screw structure of the present invention; Figure 8 This is a schematic diagram of the connection structure between the locking nut and the cotter pin of the present invention.

[0020] In the diagram: 100, upper connecting platform; 101, upper threaded hole; 200, lower connecting platform; 201, lower threaded hole; 300, adjusting sleeve; 301, locking ring; 302, stop pin; 303, cotter pin; 400, left screw; 500, right screw; 600, inner locking nut; 700, outer locking nut; 800, butterfly spring; 801, self-lubricating guide ring. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Please see Figures 1-8 As shown, a power transmission line length adjustment fitting includes: an adjustment sleeve (300) having an axially penetrating non-circular cross-section inner hole inside; The left screw 400 and the right screw 500 are inserted into the non-circular cross-section inner hole from both ends of the adjusting sleeve 300, respectively; The left screw 400 and the right screw 500 are each divided into three sections along the axial direction: The outer circumferential shape of the non-circular cross-section rod section matches the shape of the non-circular cross-section inner hole of the adjusting sleeve 300. The two form an axial sliding fit with circumferential shape locking, so that the adjusting sleeve 300 can drive the left screw 400 and the right screw 500 to rotate synchronously, while allowing the two to slide relative to each other along the axial direction. The cylindrical external thread section, located at the end away from the adjusting sleeve 300, is used for threaded engagement with external connecting parts; The transition section is located between the non-circular cross-section rod section and the cylindrical external thread section; The adjusting sleeve 300 transmits torque and restricts relative circumferential rotation only through the shape locking of the non-circular cross-section inner hole and the non-circular cross-section rod body section between it and the left screw 400 and the right screw 500. The inner wall of the adjusting sleeve 300 does not have a thread structure that mates with the cylindrical external thread section in the area corresponding to the non-circular cross-section rod body section of the left screw 400 and the right screw 500. This decouples the torque transmission function and axial guiding function of the hardware and prevents torsional loosening caused by the clearance of the thread pair under alternating loads.

[0023] In this embodiment, after applying lubricating grease to the non-circular section of the left screw 400, it is inserted into the left end of the adjusting sleeve 300 until the transition section step approaches the end face of the adjusting sleeve 300. The right screw 500 is similarly inserted into its right end. Then, the upper connecting platform 100 is screwed into the cylindrical external thread section of the left screw 400, and the lower connecting platform 200 is screwed into the cylindrical external thread section of the right screw 500. After pre-screwing to a certain depth, a wrench is used to hold the outer wall of the adjusting sleeve 300 and rotate it. Because the regular hexagonal inner hole is aligned with the... The hexagonal prism shape of the rod locks in place, and the torque of the adjusting sleeve 300 is directly transmitted to the left screw 400 and the right screw 500, forcing the two screws to rotate synchronously with the sleeve. The rotating left screw 400 is screwed into or out of the threaded hole of the upper connecting platform 100, while the right screw 500 is screwed into the lower connecting platform 200 simultaneously. This achieves stepless extension and retraction adjustment of the overall length of the fitting. After adjustment, the tension of the wire acts on the connecting platform, which transmits the tension to the screws through the threads. At this point, any wind-induced vibration load that attempts to cause relative torsion between the screws and the sleeve will be rigidly blocked by the rigid contact surface of the regular hexagonal cross section and cannot be converted into loosening displacement. This solves the problem in traditional spiral length adjustment fittings where the threaded pair simultaneously performs the dual functions of transmitting torque and axial guidance, leading to accumulated micro-motion in the threaded fit clearance under alternating loads, ultimately causing torsional loosening. By separating the guiding function from the threaded pair and giving it a non-circular cross-section shape locking structure, the relative rotation between the adjusting sleeve 300 and the left screw 400 and right screw 500 is eliminated from the kinematic source.

[0024] The non-circular cross-section inner hole is a regular hexagon, and the non-circular cross-section rod sections of the left screw 400 and right screw 500 are corresponding to regular hexagonal prisms.

[0025] In this embodiment, the most economical machining method is achieved when the inner bore of the adjusting sleeve 300 and the screw body are regular hexagonal. The threaded section can be directly machined from standard hexagonal bar stock. Furthermore, the six planes of the hexagon provide a uniform torque-transmitting contact area, making it suitable for transmission lines of conventional voltage levels. When subjected to large torque adjustments or strong vibrations, the tooth flank contact area of ​​the regular hexagon is larger than that of a circular shape, resulting in stronger resistance to compression. Additionally, the spline's centering accuracy is higher, further reducing the coaxiality deviation between the left screw 400 and right screw 500 and the adjusting sleeve 300 during rotation.

[0026] The external connector includes an upper connecting platform 100 and a lower connecting platform 200, both of which have an upper threaded hole 101 and a lower threaded hole 201 for the cylindrical external thread section to be screwed into. On the cylindrical external thread section of the left screw 400, from the adjusting sleeve 300 toward the end of the left screw 400, an inner locking nut 600, an upper connecting platform 100 and an outer locking nut 700 are sequentially fitted. On the cylindrical external thread section of the right screw 500, from the adjusting sleeve 300 toward the end of the right screw 500, an inner locking nut 600, a lower connecting platform 200 and an outer locking nut 700 are sequentially fitted. Both the inner locking nut 600 and the outer locking nut 700 are threadedly engaged with the corresponding cylindrical external thread section, and by tightening them in opposite directions, the upper connecting platform 100 or the lower connecting platform 200 is clamped and locked between the two to eliminate the thread clearance of the cylindrical external thread section and lock the axial position.

[0027] In this embodiment, the inner locking nut 600 is first screwed into the threaded section of the screw and pushed to the side close to the adjusting sleeve 300. Then, the upper connecting platform 100 is screwed in and adjusted to the approximate position of the required length. Subsequently, the outer locking nut 700 is screwed in, located at the outer end of the upper connecting platform 100. When locking, two wrenches are used to respectively clamp the inner locking nut 600 and the outer locking nut 700, applying opposing tightening torques. The inner locking nut 600 presses tightly to the right against the left end face of the upper connecting platform 100, and the outer locking nut 700 presses tightly to the left against the right end face of the upper connecting platform 100. At this time, the upper connecting platform 100 is rigidly clamped and locked by the two nuts, and the axial fit clearance between its internal threads and the screw threads is completely eliminated, forming a strong anti-loosening effect similar to double nuts against each other. By locking the inner locking nut 600 and the outer locking nut 700 against each other, the thread gap is eliminated, preventing relative rotation between the connecting table and the screw, and improving the overall stability of the hardware during long-term operation.

[0028] The diameter of the transition section cylindrical smooth rod is larger than the major diameter of the cylindrical external thread section, thus forming an annular step surface between the non-circular cross-section rod section and the cylindrical external thread section; A butterfly spring 800 is provided between the annular stepped surface and the end face of the adjusting sleeve 300; The disc spring 800 is in a compressed state when assembled, applying axial preload to the adjusting sleeve 300 to eliminate axial clearance of the non-circular cross-section mating surface and suppress slight axial movement.

[0029] In this embodiment, after the screw is fully inserted, the disc spring 800 is in a compressed, energy-storing state under the pressure of the sleeve end face and the screw step surface. When the conductor experiences axial high-frequency micro-amplitude vibration due to wind, the vibration wave attempts to drive the screw to move axially within the sleeve. The continuous axial elastic force of the disc spring 800 acts like a pre-tightened shock absorber, absorbing the axial clearance between the mating surfaces. When the screw attempts to move slightly outward, it must overcome the preload of the disc spring 800; when the screw moves slightly inward, the disc spring 800 is further compressed to provide damping. This effectively suppresses axial impact and fretting wear between the screw and the sleeve. It solves the problem of axial movement and abnormal noise caused by necessary manufacturing clearances in non-circular cross-section mating, while protecting the non-circular cross-section mating surfaces from axial impact wear.

[0030] Self-lubricating guide rings 801 are embedded at the two orifices of the non-circular cross-section inner hole of the adjusting sleeve 300; The inner cross-sectional shape of the self-lubricating guide ring 801 is consistent with the shape of the non-circular cross-section inner hole, and its material is polytetrafluoroethylene composite material.

[0031] In this embodiment, when the non-circular cross-section sections of the left screw 400 and right screw 500 slide axially within the adjusting sleeve 300, the outer surface of the screw body first contacts the inner surface of the self-lubricating guide ring 801. Since the friction coefficient of PTEE is much lower than that between metals, the rotational torque required for adjustment is significantly reduced, allowing operators to easily complete length adjustment using a regular wrench. Simultaneously, the PTEE material prevents direct metal contact between the screw body and the inner wall of the sleeve, effectively preventing fretting wear and seizing. This solves the problem that in traditional all-metal sliding fits, after long-term static pre-tightening, cold welding or adhesive wear may occur between the metal contact surfaces, leading to adjustment difficulties or even jamming. The self-lubricating guide ring 801 isolates the metal contact surfaces with a non-metallic medium, ensuring guiding accuracy while significantly improving the smoothness of adjustment and the service life of the fittings, making it particularly suitable for applications requiring regular maintenance and adjustment.

[0032] The thread pitch of the cylindrical external thread section of the left screw 400 is P1, and the thread pitch of the cylindrical external thread section of the right screw 500 is P2, and P1 is not equal to P2. With the left screw 400 and right screw 500 having different pitches, when the adjusting sleeve 300 is subjected to external vibration and has a tendency to rotate, the screws at both ends generate mutually restrictive reverse torques due to the difference in pitch, forming a differential interlocking effect.

[0033] In this embodiment, for example, the pitch P1 of the left screw 400 is 30mm, and the pitch P2 of the right screw 500 is 2.5mm. The difference between the two is approximately 16.7% of the larger pitch. When the fitting is in operation and subjected to external alternating loads such as wind vibration, if the adjusting sleeve 300 exhibits a slight rotational tendency, the left screw 400 and right screw 500 will rotate synchronously with the adjusting sleeve 300 through their non-circular cross-sections, resulting in a rotational feed tendency in the upper connecting platform 100 and the lower connecting platform 200, respectively. However, due to the different pitches at both ends, at the same rotation angle, the axial displacement (P1×θ / 360°) that the left screw 400 attempts to generate is not equal to the axial displacement (P2×θ / 360°) that the right screw 500 attempts to generate. This displacement difference generates mutually restraining reverse torques within the internal structure of the fitting. The rotational tendency of one screw is offset by the asynchronous resistance generated by the pitch difference of the other screw. This creates a differential interlocking effect: even if the anti-rotation capability of the non-circular cross-section guide structure is overcome under certain extreme overload conditions, the differential thread can provide a final line of defense through the mutual cancellation of the torques at both ends, preventing the left screw 400 and the right screw 500 from retracting simultaneously.

[0034] The outer surfaces of both ends of the adjusting sleeve 300 are machined with external threads, and locking rings 301 are fitted on the external threads; The locking ring 301 has an internal thread and can be screwed in axially along the adjusting sleeve 300 to press the transition end face of the left screw 400 or the right screw 500 to achieve strong axial locking.

[0035] The sidewall of the locking ring 301 is provided with a radial pin hole corresponding to the sidewall of the adjusting sleeve 300. A stop pin 302 is inserted into the radial pin hole. The tail of the stop pin 302 is provided with a radial small hole. A cotter pin 303 is inserted into the radial small hole. The two metal wires of the cotter pin 303 pass through the radial small hole and bend in opposite directions. The outer dimension of the bent metal wire is larger than the diameter of the radial through hole on the locking ring 301. The bent metal wire ends abut against the outer wall surface of the locking ring 301 to prevent the stop pin 302 from axially dislodging from the radial through hole.

[0036] In this embodiment, after the fitting length is adjusted to the correct position, the operator screws the locking ring 301 along the external thread of the adjusting sleeve 300 towards the screw until the inner end face of the locking ring 301 presses against the annular stepped surface of the transition section of the left screw 400 (or right screw 500). The axial clamping force applied by the locking ring 301 to the stepped surface of the screw firmly fixes the screw in its axial position. To further prevent the locking ring 301 from loosening due to vibration, after the stop pin 302 is inserted into place, the radial hole exposed at its tail is located near the outer wall of the locking ring 301. The cotter pin 303 is passed through this hole, and the two strands of metal wire of the cotter pin 303 are bent upwards and downwards by about 60° to 90° respectively, so that they are close to the outer wall surface of the locking ring 301. At this time, the width of the bent part of the cotter pin 303 is greater than the diameter of the radial through hole on the locking ring 301. When the stop pin 302 is subjected to an outward force, the bent cotter pin 303 is blocked by the outer wall of the locking ring 301 and cannot pass through the radial through hole, thereby reliably locking the stop pin 302 in the hole.

[0037] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A transmission line length adjustment fitting, characterized in that: include: The adjusting sleeve (300) has an axially penetrating non-circular cross-section inner hole; The left screw (400) and the right screw (500) are respectively inserted into the non-circular cross-section inner hole from both ends of the adjusting sleeve (300); The left screw (400) and right screw (500) are each divided into three sections along the axial direction: The outer circumferential shape of the non-circular cross-section rod section matches the shape of the non-circular cross-section inner hole of the adjusting sleeve (300), and the two form an axial sliding fit with circumferential shape locking, so that the adjusting sleeve (300) can drive the left screw (400) and the right screw (500) to rotate synchronously, while allowing the two to slide relative to each other along the axial direction; The cylindrical external thread section, located at the end away from the adjusting sleeve (300), is used for threaded engagement with an external connector; The transition section is located between the non-circular cross-section rod section and the cylindrical external thread section; The adjusting sleeve (300) transmits torque and restricts relative circumferential rotation only through the shape locking of the non-circular cross-section inner hole and the non-circular cross-section rod body section between the left screw (400) and the right screw (500). The inner wall of the adjusting sleeve (300) does not have a thread structure that mates with the cylindrical external thread section in the area corresponding to the non-circular cross-section rod body section of the left screw (400) and the right screw (500), thereby decoupling the torque transmission function and axial guiding function of the fitting and preventing torsional loosening caused by the thread pair clearance under alternating loads.

2. The transmission line length adjustment fitting according to claim 1, characterized in that: The non-circular cross-section inner hole is a regular hexagon, and the non-circular cross-section rod sections of the left screw (400) and right screw (500) are corresponding to regular hexagonal prisms.

3. The transmission line length adjustment fitting according to claim 1, characterized in that: The external connector includes an upper connecting platform (100) and a lower connecting platform (200), both of which have an upper threaded hole (101) and a lower threaded hole (201) for the cylindrical external thread section to be screwed into. On the cylindrical external thread section of the left screw (400), from the adjusting sleeve (300) toward the end of the left screw (400), an inner locking nut (600), the upper connecting platform (100) and an outer locking nut (700) are sequentially fitted. On the cylindrical external thread section of the right screw (500), from the adjusting sleeve (300) toward the end of the right screw (500), an inner locking nut (600), the lower connecting platform (200) and an outer locking nut (700) are sequentially fitted. The inner locking nut (600) and the outer locking nut (700) are both threadedly engaged with the corresponding cylindrical external thread section, and by tightening them in opposite directions, the upper connecting platform (100) or the lower connecting platform (200) is clamped and locked between the two to eliminate the thread gap of the cylindrical external thread section and lock the axial position.

4. The transmission line length adjustment fitting according to claim 1, characterized in that: The diameter of the transition section cylindrical smooth rod segment is larger than the major diameter of the cylindrical external thread segment, thereby forming an annular step surface between the non-circular cross-section rod segment and the cylindrical external thread segment; A butterfly spring (800) is provided between the annular stepped surface and the end face of the adjusting sleeve (300). The disc spring (800) is in a compressed state when assembled, and applies an axial preload to the adjusting sleeve (300) to eliminate the axial clearance of the non-circular cross-section mating surface and suppress slight axial movement.

5. The transmission line length adjustment fitting according to claim 1, characterized in that: The two openings of the non-circular cross-section inner hole of the adjusting sleeve (300) are fitted with self-lubricating guide rings (801). The inner cross-sectional shape of the self-lubricating guide ring (801) is consistent with the shape of the non-circular cross-sectional inner hole, and its material is polytetrafluoroethylene composite material.

6. The transmission line length adjustment fitting according to claim 1, characterized in that: The thread pitch of the cylindrical external thread section of the left screw (400) is P1, and the thread pitch of the cylindrical external thread section of the right screw (500) is P2, and P1 is not equal to P2. When the adjusting sleeve (300) is subjected to external vibration and has a tendency to rotate, the left screw (400) and right screw (500) with different pitches generate mutually restrictive reverse torques due to the pitch difference, forming a differential interlocking effect.

7. The transmission line length adjustment fitting according to claim 1, characterized in that: The outer surfaces of both ends of the adjusting sleeve (300) are machined with external threads, and locking rings (301) are fitted on the external threads. The locking ring (301) has an internal thread and can be screwed in axially along the adjusting sleeve (300) to press the transition end face of the left screw (400) or the right screw (500) to achieve axial strong locking.

8. A transmission line length adjustment fitting according to claim 7, characterized in that: The sidewall of the locking ring (301) and the sidewall of the adjusting sleeve (300) are provided with radial pin holes, and a stop pin (302) is inserted into the radial pin hole. The tail of the stop pin (302) is provided with a radial small hole, and a cotter pin (303) is inserted into the radial small hole. The two metal wires of the cotter pin (303) pass through the radial small hole and bend in opposite directions. The outer dimension of the bent wire is larger than the diameter of the radial through hole on the locking ring (301), and the end of the bent metal wire abuts against the outer wall surface of the locking ring (301) to prevent the stop pin (302) from axially dislodging from the radial through hole.

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