A dancing leg kicking training device

Abstract

The application discloses a dance leg kicking training device, which comprises a C-shaped bottom frame, liftable handrails installed on the left and right sides of the top of the C-shaped bottom frame, and a double-column stand fixed on the top of the C-shaped bottom frame between the two liftable handrails. Two housings in mirror-symmetrical structures are installed on the outer wall of one side of the double-column stand. A rotating shaft is rotatably installed at the lower position in the housing. A foot-binding rocker structure is installed on the end of the rotating shaft close to the liftable handrail. An angle gauge for marking the swing angle of the foot-binding rocker structure is installed on the outer wall close to the liftable handrail of the two liftable handrails. The application can cultivate the motion coordination and body control ability of the trainees through the instant physical band training feedback mechanism, so that the trainees can intuitively feel the force speed and angle change of the trainer, and the interactivity and real-time feedback effect of the training are enhanced.

Description

Technical Field

[0001] This invention relates to the field of dance training equipment technology, specifically a dance kicking training device. Background Technology

[0002] Dance kicking and leg-lifting training equipment plays a crucial role in improving dancers' technique. It primarily helps dancers enhance leg muscle strength and joint flexibility, thereby increasing the height and precision of movements. This equipment includes wall-mounted barres that provide a solid foundation for dynamic balance and static leg extension; flexible resistance bands that help dancers safely exceed their daily range of motion during floor practice to pursue maximum range of motion; and elastic strength training bands that create continuous resistance in side kicks and back kicks, thus honing muscle control and endurance. More complex multi-functional training equipment integrates pulleys and weights, enabling multi-angle, all-around resistance training. During training, users rely on the barres for basic control exercises to establish correct force perception and body balance. They then use resistance bands for passive stretching to gently expand the extensibility of joints and ligaments, ultimately transitioning to actively resisting various resistance bands. Through repetitive and loaded kicking movements, they forge deep strength and dynamic control capabilities sufficient to support high-speed, high-amplitude technical movements.

[0003] As disclosed in CN115779347B, a dance kicking training device and method includes a support frame, a rolling element, a traction rope, a leg fixing component, a drive mechanism, and a sensor assembly. The rolling element is disposed on the support frame. The first end of the traction rope is wound around the rolling element, and the second end is connected to the leg fixing component. The drive mechanism is disposed on the support frame and connected to the rolling element, and is used to drive the rolling element to roll, so that the traction rope contracts or extends, thereby raising or lowering the leg. The sensor assembly is disposed at a distance from the support frame and electrically connected to the drive mechanism. It mainly drives the rolling element to roll through the drive mechanism, so that the traction rope contracts or extends, thereby raising or lowering the leg. The sensor assembly senses when the leg kicks to a preset angle. The device component controls the drive mechanism to remain stationary so that the leg can stay at a preset angle. This shows that the above technical solution provides the user with the requirement to keep the leg still when kicking to a preset angle during single training. However, in two-person training, the user can only rely on vision and personal perception to understand the coach's leg lifting speed and angle. The coach uses verbal instructions, such as "higher" or "slower," or provides manual assistance, that is, personally guiding or supporting the student's leg with their hands. For the student, understanding this information is challenging, making the student's understanding of "standard" entirely based on the coach's guidance and their own immediate, possibly inaccurate, physical sensations. It is difficult to establish a stable and accurate muscle memory and movement model. Summary of the Invention

[0004] The purpose of this invention is to provide a dance kicking training device. In single-person training, the student stands on one side of one of the adjustable armrests, with their feet positioned at the foot-binding rocker arm structure. The student kicks or lifts their leg to apply force to the foot-binding rocker arm structure, causing a rotating shaft in one of the outer shells to rotate. At this time, a magnetic adjustment structure and a magnetic resistance structure within the outer shells apply resistance to the rotation of the shaft. A protractor indicates the lifting angle of the foot-binding rocker arm structure each time. In two-person training, the instructor stands at the other foot-binding rocker arm structure. The opposite ends of the two rotating shafts on the left and right sides are connected by a spline coupling. After the instructor lifts their leg, both rotating shafts rotate together. The student can then perceive the speed and angle of the instructor's leg force, thereby solving the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a dance kicking training device, comprising a C-shaped base frame, liftable handrails installed on the left and right sides of the top of the C-shaped base frame, and a double-column upright fixed to the top of the C-shaped base frame between the two liftable handrails. Two mirror-symmetrical shells are installed on one outer wall of the double-column upright. A rotating shaft is rotatably installed at the lower position inside the shell. A foot-binding rocker arm structure is installed at the end of the rotating shaft near the liftable handrail. A protractor for marking the swing angle of the foot-binding rocker arm structure is installed on the adjacent outer walls of the two liftable handrails. A magnetic resistance structure connected to the rotating shaft is provided inside the shell. A magnetic adjustment structure is installed on the inclined outer wall of the shell away from the double-column upright. A spline coupling is installed between the opposite ends of the two rotating shafts.

[0006] Preferably, the magnetic resistance structure includes a steel pipe inclinedly fixed to the inner wall of one side of the outer shell, and a lower cross wheel frame and an upper cross wheel frame fixed at the upper and lower positions inside the outer shell, respectively. The upper cross wheel frame has a drive pulley shaft rotatably installed inside, and a flywheel is fixed on the surface of the drive pulley shaft. A ball bearing is installed at the center position inside the lower cross wheel frame, and the shaft is installed in the inner ring of the ball bearing. A main pulley is fixed at one end of the surface of the shaft, and a transmission belt is installed between the main pulley and the flywheel.

[0007] Preferably, a tensioner for keeping the drive belt taut is installed on one side of the outer wall of the upper cross wheel frame.

[0008] Preferably, a U-shaped arm is fixed to the outer wall of the double-column upright above the two outer shells, and the upper end of the steel pipe extends through to the outside of the outer shell and is connected to the lower surface of the U-shaped arm.

[0009] Preferably, the magnetic adjustment structure includes an internal threaded sleeve fixed on the inclined outer wall of the outer shell and a threaded shaft installed inside the internal threaded sleeve. One end of the threaded shaft passes through the outside of the steel pipe and is provided with a magnetic block. The magnetic block and the threaded shaft are rotatably connected. The other end of the threaded shaft is fixed with a knob.

[0010] Preferably, the tensioner includes a pull arm hinged to the outer wall of one side of the upper cross wheel frame and a tension spring hooked to the upper end of the pull arm. The end of the tension spring away from the pull arm is hooked to the outer wall of the upper cross wheel frame. A roller is rotatably mounted on the lower end of the pull arm, and the roller and the transmission belt abut against each other.

[0011] Preferably, the foot-type rocker arm structure includes a U-shaped arm fixed to one end of the rotating shaft, a lower sponge roller fixed to the lower end of the U-shaped arm, and an upper rubber-coated beam installed inside the U-shaped arm above the lower sponge roller, with a cavity provided between the upper rubber-coated beam and the lower sponge roller.

[0012] Preferably, the U-shaped arm is made of a hard plastic component.

[0013] Preferably, the spline coupling includes a hollow key shaft fixed on the opposite ends of two rotating shafts and an external spline shaft slidably installed inside one of the hollow key shafts. The outer wall of the external spline shaft is provided with an internal threaded rear hole, and a locking pin is installed on the outer wall of the hollow key shaft for threaded engagement with the internal threaded rear hole.

[0014] Compared with the prior art, the beneficial effects of this invention are as follows: This dance kicking training device, through the coordinated structure of a liftable armrest, two outer shells on the left and right sides, a rotating shaft, a foot-binding rocker arm structure, a magnetic resistance structure, a magnetic adjustment structure, and a spline coupling, allows the student to stand on one side of one of the liftable armrests, with their feet positioned at the foot-binding rocker arm structure. Kicking or lifting the leg applies force to the foot-binding rocker arm structure, causing the rotating shaft in one of the outer shells to rotate. At this time, the magnetic adjustment structure and the magnetic resistance structure within the outer shells apply resistance to the rotation of the shaft. A protractor marks each foot-binding movement. The lifting angle of the type-shaped rocker arm structure allows for two-person training. The instructor is positioned at the other foot-binding rocker arm structure, with the two rotating shafts on opposite sides connected by a spline coupling. When the instructor lifts their leg, both shafts rotate together. Since the student's foot is also within the foot-binding rocker arm structure, both students' leg movements rotate synchronously. At this time, the student can perceive the speed and angle of the instructor's leg force, thereby cultivating the student's motor coordination and body control through an instant physical training feedback mechanism. This allows the student to intuitively feel the changes in the instructor's force speed and angle, enhancing the interactivity and real-time feedback effect of the training.

[0015] Traditional two-person coaching relies on visual observation and verbal instruction, making it difficult for trainees to accurately grasp subtle changes in the coach's movements. This solution uses mechanical transmission to physically map the coach's movements to the trainee's side. Trainees can perceive the coach's force and speed through tactile and force sensation in their legs, compensating for the lack of visual and auditory information. This makes the training process more immersive and coordinated, allowing for more precise adjustments to their movements and achieving more efficient training results. Secondly, the magnetic adjustment structure and magnetic resistance structure provide an adjustable resistance environment for training. Whether on the trainee's or coach's side, the rotating shaft is controlled by resistance during rotation. This resistance not only increases the intensity of training but also effectively prevents movements from being too fast or too violent, ensuring training safety. The smooth adjustment characteristics of the magnetic resistance also make the movement process smoother, reducing mechanical impact and improving user comfort. At the same time, the protractor's marking function provides both parties with intuitive angle references, helping trainees and coaches understand the range of motion in real time, facilitating adjustments based on training needs.

[0016] Finally, the mechanical linkage structure of this design simplifies the technical implementation of two-person training, reduces the reliance on complex electronic sensors and feedback systems, and the use of spline couplings ensures synchronous rotation between shafts. The structure is compact, durable, and suitable for frequent training use. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the three-dimensional structure of the present invention. Figure 1 ;

[0018] Figure 2 This is a schematic diagram of the three-dimensional structure of the present invention. Figure 2 ;

[0019] Figure 3 This is a side cross-sectional view of the present invention.

[0020] Figure 4 This is a three-dimensional cross-sectional structural diagram of the present invention;

[0021] Figure 5 This is a schematic diagram of the three-dimensional structure of the present invention. Figure 3 ;

[0022] Figure 6 This is a three-dimensional cross-sectional view of the magnetic resistance rotation structure of the present invention;

[0023] Figure 7 This is a schematic diagram of the three-dimensional cross-sectional structure of the C-shaped bottom frame of the present invention;

[0024] Figure 8 For the present invention Figure 5 Enlarged structural diagram at point A in the middle;

[0025] Figure 9This is a three-dimensional structural diagram of the foot-type rocker arm structure of the present invention.

[0026] In the diagram: 1. C-shaped base frame; 2. Adjustable handrail frame; 3. Double-column upright frame; 301. U-shaped arm; 4. Outer shell; 5. Magnetic resistance structure; 501. Steel pipe; 502. Lower cross wheel frame; 503. Ball bearing; 504. Main pulley; 505. Upper cross wheel frame; 506. Flywheel; 507. Drive belt; 508. Tensioner; 509. Drive pulley shaft; 6. Magnetic adjustment structure 601. Internal threaded sleeve; 602. Threaded shaft; 603. Magnetic block; 604. Knob; 7. Rotating shaft; 8. Traction-foot type rocker arm structure; 801. U-shaped arm; 802. Lower sponge roller; 803. Upper rubber-coated beam; 804. Cavity; 9. Protractor; 10. Splined coupling; 1001. Hollow key shaft; 1002. External spline shaft; 1003. Locking pin; 1004. Internal threaded rear hole. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0028] Example 1, by Figures 1 to 5 The present invention includes a C-shaped base frame 1, liftable handrails 2 installed on the left and right sides of the top of the C-shaped base frame 1, and a double-column upright frame 3 fixed to the top of the C-shaped base frame 1 between the two liftable handrails 2. Two mirror-symmetrical shells 4 are installed on one outer wall of the double-column upright frame 3. A rotating shaft 7 is rotatably installed at the lower position inside the shell 4. A foot-binding rocker arm structure 8 is installed at the end of the rotating shaft 7 near the liftable handrail 2. A protractor 9 for marking the swing angle of the foot-binding rocker arm structure 8 is installed on the adjacent outer walls of the two liftable handrails 2. A magnetic resistance structure 5 connected to the rotating shaft 7 is provided inside the shell 4. A magnetic adjustment structure 6 is installed on the inclined outer wall of the shell 4 away from the double-column upright frame 3. A spline coupling 10 is installed between the opposite ends of the two rotating shafts 7. Even when the spline coupling 10 is not connected to the two rotating shafts 7, the device can still meet the needs of two-person training.

[0029] Example 2, based on Example 1, is... Figure 6The magnetic resistance structure 5 includes a steel pipe 501 inclinedly fixed to the inner wall of one side of the outer casing 4, and a lower cross wheel frame 502 and an upper cross wheel frame 505 fixed at upper and lower positions inside the outer casing 4, respectively. A drive pulley shaft 509 is rotatably mounted inside the upper cross wheel frame 505, and a flywheel 506 is fixed to the surface of the drive pulley shaft 509. A ball bearing 503 is installed at the center position inside the lower cross wheel frame 502, and a rotating shaft 7 is installed in the inner ring of the ball bearing 503. A main belt pulley 504 is fixed to one end of the surface of the rotating shaft 7. The main belt pulley 504 and the flywheel 506... A transmission belt 507 is installed between them. When the user is training alone, the user's feet are located at the lower end of the foot-binding rocker arm structure 8. When the user kicks or lifts his leg, the foot-binding rocker arm structure 8 will drive the rotating shaft 7 and the main belt pulley 504 to rotate, thereby driving the active pulley shaft 509 and the flywheel 506 to rotate through the transmission belt 507. After the kick or lift reaches the end position, the foot-binding rocker arm structure 8 will swing back to its original position under the action of gravity. The magnetic resistance structure 5 generates resistance through the magnetic field to ensure the smoothness and stability of the rotating shaft during rotation, and avoid injury caused by excessively fast movements or sudden acceleration.

[0030] The magnetic adjustment structure 6 includes an inner threaded sleeve 601 fixed on the inclined outer wall of the outer shell 4 and a threaded shaft 602 installed inside the inner threaded sleeve 601. One end of the threaded shaft 602 passes through the outside of the steel pipe 501 and is provided with a magnetic block 603. The magnetic block 603 and the threaded shaft 602 are rotatably connected. The other end of the threaded shaft 602 is fixed with a knob 604. When adjusting the rotational resistance of the flywheel 506 through the magnetic adjustment structure 6, the user drives the threaded shaft 602 to rotate through the knob 604 according to their own needs. This causes the threaded shaft 602 to drive the magnetic block 603 to move along the central axis of the inner threaded sleeve 601. When the magnetic block 603 approaches the flywheel 506, the rotational resistance of the flywheel 506 increases. At this time, the user's legs need to apply more force to the foot-binding rocker arm structure 8 to drive the rotating shaft 7 to rotate. Thus, the resistance can be adjusted according to the user's own training needs to achieve personalized training intensity.

[0031] A tensioner 508 is installed on one outer wall of the upper cross pulley frame 505 to keep the transmission belt 507 taut. The tensioner 508 includes a pull arm hinged to the outer wall of the upper cross pulley frame 505 and a tension spring hooked to the upper end of the pull arm. The end of the tension spring away from the pull arm is hooked to the outer wall of the upper cross pulley frame 505. A roller is rotatably installed at the lower end of the pull arm. The roller and the transmission belt 507 abut against each other. The tensioner 508 keeps the transmission belt 507 taut, so that the main pulley 504 and the flywheel 506 maintain stable power transmission.

[0032] A U-shaped arm 301 is fixed on the outer wall of the double-column support 3 above the two outer shells 4. The upper end of the steel pipe 501 extends through the outside of the outer shell 4 and is connected to the lower surface of the U-shaped arm 301.

[0033] Example 3, based on Example 2, by Figure 7 , Figure 8 and Figure 9 The given is that the foot-type rocker arm structure 8 includes a U-shaped arm 801 fixed to one end of the rotating shaft 7, a lower sponge roller 802 fixed to the lower end of the U-shaped arm 801, and an upper rubber-coated beam 803 installed inside the U-shaped arm 801 above the lower sponge roller 802. A cavity 804 is provided between the upper rubber-coated beam 803 and the lower sponge roller 802. The U-shaped arm 801 is made of a component made of hard plastic material.

[0034] During single-person training, the user's feet are positioned below the lower sponge roller 802. At this time, the user's legs drive the rotating shaft 7 to rotate via the lower sponge roller 802 and the U-shaped arm 801. During two-person training, the user's feet are positioned in the cavity 804 between the upper rubber-coated beam 803 and the lower sponge roller 802, so that the coach can drive the U-shaped arm 801 to swing via the spline coupling 10 and the rotating shaft 7.

[0035] The spline coupling 10 includes a hollow key shaft 1001 fixed to the opposite ends of two rotating shafts 7, and an external spline shaft 1002 slidably mounted inside one of the hollow key shafts 1001. The outer wall of the external spline shaft 1002 has an internally threaded rear hole 1004. A locking pin 1003 for threaded engagement with the internally threaded rear hole 1004 is mounted on the outer wall of the hollow key shaft 1001. In the case of two-person training, the user will remove the locking pin 1003 from the external spline shaft 1002 and the hollow key shaft 7. Unscrew 001, then pull the external spline shaft 1002 to slide, so that the end of the external spline shaft 1002 away from the hollow key shaft 1001 enters the spline coupling 10 at the end of another rotating shaft 7. That is, the two hollow key shafts 1001 are connected by the external spline shaft 1002. At this time, the internal thread rear hole 1004 on the outside of the external spline shaft 1002 also moves forward a distance. The user can then screw the locking pin 1003 into the internal thread rear hole 1004 of the external spline shaft 1002.

[0036] In this embodiment, the user first stands on one side of one of the adjustable handrails 2, holding the handrails 2 with both hands or one hand, keeping the body upright and shoulders relaxed, preparing for the kicking motion. The adjustable handrails 2 are suitable for users of different heights, maintaining the stability of the user's posture during training and reducing the risk of sports injuries caused by instability. Then, the user places one foot on the foot-binding rocker arm structure 8. The user applies force to the foot-binding rocker arm structure 8 by kicking or lifting the leg, causing the pivot 7 to rotate. At this time, the magnetic adjustment structure 6 and the magnetic resistance structure 5 in the outer shell 4 come into play. The controllable magnetic field they generate forms a smooth and continuous resistance to the rotation of the pivot 7. This force is clearly fed back to the user's leg, simulating the self-gravity and muscle strength resistance that needs to be overcome in real dance. Throughout the training process, the user's eyes can be focused on the protractor at any time, which clearly displays the precise angle of the current leg lift in real time, thus allowing for the assessment based on objective data. Control your own range of motion; during partner training, the instructor stands on the other side at the foot-binding rocker arm structure 8. The two rotating shafts 7 are connected by a spline coupling 10, making the training units of the two people a unified mechanical whole. When the instructor begins to lift his leg, all the details of his movement, including the initial explosive force of the leg lift, the stable speed during the lift, the subtle pause at the target angle, and the control force during the lowering, are transmitted in real time and without loss to the rotating shaft 7 and foot-binding rocker arm structure 8 on the student's side through the spline coupling 10. The user can feel the speed and angle changes of the instructor's leg force. By changing the rhythm and range of his own movements, the instructor guides the student to safely explore the limits of their ability, achieving efficient imitation and skill transfer. After training, the user should perform appropriate stretching and relaxation to relieve muscle tension, promote blood circulation, and reduce post-training soreness. The height adjustment function of the height-adjustable handrail 2 also makes it convenient for the user to adjust their posture and perform auxiliary stretching movements.

[0037] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0038] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A dance kicking training device, comprising a C-shaped base frame (1), liftable handrails (2) installed on the left and right sides of the top of the C-shaped base frame (1), and a double-column upright frame (3) fixed to the top of the C-shaped base frame (1) between the two liftable handrails (2), characterized in that: Two mirror-symmetrical shells (4) are installed on one side of the outer wall of the double-column upright (3). A rotating shaft (7) is rotatably installed at the lower position inside the shell (4). A foot-binding rocker arm structure (8) is installed at the end of the rotating shaft (7) near the lifting handrail (2). A protractor (9) for marking the swing angle of the foot-binding rocker arm structure (8) is installed on the outer wall of the two lifting handrails (2) that are close to each other. A magnetic resistance structure (5) connected to the rotating shaft (7) is provided inside the shell (4). A magnetic adjustment structure (6) is installed on the inclined outer wall of the shell (4) away from the double-column upright (3). A spline coupling (10) is installed between the opposite ends of the two rotating shafts (7). When two people are training together, the coach is located at the other foot-binding rocker arm structure (8), and the opposite ends of the two rotating shafts (7) on the left and right sides are connected by the spline coupling (10).

2. The dance kicking training device according to claim 1, characterized in that: The magnetic resistance structure (5) includes a steel pipe (501) that is inclined and fixed on the inner wall of one side of the outer shell (4) and a lower cross wheel frame (502) and an upper cross wheel frame (505) that are respectively fixed at the upper and lower positions inside the outer shell (4). The upper cross wheel frame (505) has a drive pulley shaft (509) rotatably installed inside, and a flywheel (506) is fixed on the surface of the drive pulley shaft (509). A ball bearing (503) is installed at the center position inside the lower cross wheel frame (502). The rotating shaft (7) is installed in the inner ring of the ball bearing (503). A main belt pulley (504) is fixed at one end of the surface of the rotating shaft (7). A transmission belt (507) is installed between the main belt pulley (504) and the flywheel (506).

3. The dance kicking training device according to claim 2, characterized in that: A tensioner (508) for keeping the transmission belt (507) taut is installed on one side of the outer wall of the upper cross wheel frame (505).

4. The dance kicking training device according to claim 2, characterized in that: A U-shaped arm (301) is fixed on the outer wall of the double-column support (3) above the two outer shells (4). The upper end of the steel pipe (501) extends through the outside of the outer shell (4) and is connected to the lower surface of the U-shaped arm (301).

5. The dance kicking training device according to claim 2, characterized in that: The magnetic adjustment structure (6) includes an internal threaded sleeve (601) fixed on the inclined outer wall of the outer shell (4) and a threaded shaft (602) installed inside the internal threaded sleeve (601). One end of the threaded shaft (602) passes through the outside of the steel pipe (501) and is provided with a magnetic block (603). The magnetic block (603) and the threaded shaft (602) are rotatably connected. The other end of the threaded shaft (602) is fixed with a knob (604).

6. The dance kicking training device according to claim 3, characterized in that: The tensioner (508) includes a pull arm hinged to the outer wall of one side of the upper cross wheel frame (505) and a tension spring hooked to the upper end of the pull arm. The end of the tension spring away from the pull arm is hooked to the outer wall of the upper cross wheel frame (505). A roller is rotatably mounted on the lower end of the pull arm, and the roller and the transmission belt (507) abut against each other.

7. The dance kicking training device according to claim 1, characterized in that: The foot-type rocker arm structure (8) includes a U-shaped arm (801) fixed to one end of the rotating shaft (7), a lower sponge roller (802) fixed to the lower end of the U-shaped arm (801), and an upper rubber-coated beam (803) installed inside the U-shaped arm (801) above the lower sponge roller (802). A cavity (804) is provided between the upper rubber-coated beam (803) and the lower sponge roller (802).

8. The dance kicking training device according to claim 7, characterized in that: The U-shaped arm (801) is made of a hard plastic component.

9. A dance kicking training device according to claim 7, characterized in that: The spline coupling (10) includes a hollow key shaft (1001) fixed on the opposite ends of two rotating shafts (7) and an external spline shaft (1002) slidably mounted inside one of the hollow key shafts (1001). The outer wall of the external spline shaft (1002) is provided with an internal threaded rear hole (1004). The outer wall of the hollow key shaft (1001) is provided with a locking pin (1003) for threaded engagement with the internal threaded rear hole (1004).

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