Tool holder for double-hole blade and turning tool

Abstract

The invention discloses a tool holder for a double-hole blade and a turning tool, the tool holder for the double-hole blade comprises a tool holder mounting portion and a tool holder locking portion, the mounting upper surface of the tool holder mounting portion intersects with the locking front side surface of the tool holder locking portion to form an accommodating area for the double-hole blade, and an elastic groove is provided at the intersection, two blade limiting platforms perpendicular to the mounting upper surface and corresponding to the two positioning holes of the double-hole blade are provided on the mounting upper surface, two tool holder limiting holes penetrating its positioning lower surface and the mounting upper surface are provided on the tool holder mounting portion, a double-head screw accommodating groove is provided on the locking rear side surface of the tool holder locking portion, the distance between the locking front side surface and the proximal edge of the blade limiting platform is W1, the distance between the blade main side surface of the double-hole blade matched with the locking front side surface and the proximal edge of the positioning hole of the double-hole blade is W2, W1<W2, 0.05mm≤W2-W1≤0.5mm, the invention has the advantages of large clamping force on the blade, stable clamping, good processing quality, etc.

Description

Technical Field

[0001] The invention mainly relates to the field of metal cutting, and in particular to a tool holder of a double-hole blade and a turning tool. Background Art

[0002] In the metal turning industry, especially in gravity turning, due to the large cutting depth and large blade size, double-hole structure blades are usually used. Correspondingly, the turning tool adopts a lever structure to clamp the turning blade, but the clamping force of the lever structure is limited. The cutting force and cutting vibration are large during the cutting process, which can easily cause the blade to loosen and fail due to insufficient clamping force, affecting the processing quality and blade life. Summary of the invention

[0003] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a tool holder with a double-hole blade having a large clamping force and stable clamping, and a turning tool with a compact structure, stable and reliable structure and good processing quality.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] A tool clamp for a double-hole blade, comprising an integrated tool clamp mounting portion and a tool clamp locking portion, the mounting upper surface of the tool clamp mounting portion intersecting with the locking front side surface of the tool clamp locking portion to form a accommodating area for the double-hole blade, and an elastic groove is provided at the intersection, the mounting upper surface is provided with two blade limit platforms perpendicular to the mounting upper surface and corresponding to the two positioning holes of the double-hole blade, the tool clamp mounting portion is provided with at least two tool clamp limit holes that penetrate its positioning lower surface and the mounting upper surface, the locking rear side surface of the tool clamp locking portion is provided with a double-headed screw accommodating groove, the distance between the locking front side surface and the proximal edge of the blade limit platform is W1, the distance between the main side surface of the blade that cooperates with the locking front side surface of the double-hole blade and the proximal edge of the positioning hole of the double-hole blade is W2, which should satisfy: W1<W2, 0.05mm≤W2-W1≤0.5mm.

[0006] As a further improvement of the above technical solution:

[0007] The installation upper surface and the positioning lower surface, the installation front side surface and the installation rear side surface, the installation left side surface and the installation right side surface of the tool clamp mounting part are parallel to each other, the locking front side surface and the locking rear side surface of the tool clamp locking part are parallel to each other and perpendicular to the installation upper surface, and the locking left side surface and the locking right side surface of the tool clamp locking part are parallel.

[0008] The distances between the installation rear side surface, the locking front side surface, and the locking rear side surface and the installation front side surface are L1, L2, and L3, respectively, and should satisfy: L2<L1<L3.

[0009] The distance between the locking left side and the locking right side is the same as the left-right length of the double-hole blade, and the installation right side is located to the right of the locking right side so that the right side of the tool holder installation portion forms a tool groove positioning portion.

[0010] The blade limit platform includes an upper limit portion and a lower limit portion, both of which are cylindrical and have diameters of d1 and d2 respectively. The diameter of the positioning hole is D, which should satisfy: d2<d1<D. The height of the upper limit portion is H, which should satisfy: 1mm≤H≤5mm.

[0011] A turning tool comprises a tool body, a double-hole blade, a limit screw, a double-head screw and a tool holder for the above-mentioned double-hole blade, the double-hole blade being mounted on the tool holder, the two positioning holes respectively cooperating with the two blade limit platforms, the tool holder being mounted in a tool groove of the tool body, a screw hole corresponding to the tool holder limit hole being provided on the bottom surface of the tool groove, a double-head screw hole corresponding to the double-head screw accommodating groove being provided on the main side wall of the tool groove, the limit screw passing through the tool holder limit hole and cooperating with the screw hole, and two ends of the double-head screw respectively cooperating with the double-head screw hole and the double-head screw accommodating groove.

[0012] As a further improvement of the above technical solution:

[0013] The right side surface of the double-hole blade cooperates with the upper part of the right side wall of the blade groove. The center of the positioning hole of the double-hole blade and the center of the blade limit platform have an eccentricity E in a direction perpendicular to the installation right side surface, which should satisfy: 0.05mm≤E≤0.5mm.

[0014] The positioning lower surface of the tool clamp cooperates with the bottom surface of the tool groove, the locking rear side surface of the tool clamp cooperates with the clearance of the upper part of the main side wall of the tool groove, the installation rear side surface of the tool clamp cooperates with the lower part of the main side wall of the tool groove, the lower part of the right side wall of the tool groove is recessed to the right to form a positioning groove, and the tool groove positioning part cooperates with the positioning groove.

[0015] Two locking screw holes are also provided on the main side wall of the knife groove, and the two locking screws are respectively installed in the locking screw holes and the ends thereof are in contact with the locking rear side surface.

[0016] The stud screw comprises a screw driving part, a screw neck and a screw limiting part in sequence. The stud screw accommodating groove also comprises a neck cavity. The screw limiting part is installed in the stud screw accommodating groove. The screw driving part is provided with an external thread and cooperates with the stud screw hole. The screw neck is located in the neck cavity. The diameters of the screw driving part, the screw neck and the screw limiting part are D1, D2 and D3 respectively. The diameter of the neck cavity is dx, which should satisfy: D2<D1, D2<D3, D2<dx<D3.

[0017] Compared with the prior art, the advantages of the present invention are:

[0018] (1) The tool holder of the double-hole blade of the present invention comprises an integrated tool holder mounting portion and a tool holder locking portion, wherein the mounting upper surface of the tool holder mounting portion intersects with the locking front side surface of the tool holder locking portion to form a receiving area for the double-hole blade, and an elastic groove is provided at the intersection, and two blade limiting platforms perpendicular to the mounting upper surface and corresponding to the two positioning holes of the double-hole blade are provided on the mounting upper surface, and at least two tool holder limiting holes penetrating its positioning lower surface and the mounting upper surface are provided on the tool holder mounting portion, and a stud screw receiving groove is provided on the locking rear side surface of the tool holder locking portion, and the distance between the locking front side surface and the proximal edge of the blade limiting platform is W1, and the double-hole blade is matched with the locking front side surface. The distance between the main side of the combined blade and the proximal edge of the positioning hole of the double-hole blade is W2, which should satisfy: W1<W2, 0.05mm≤W2-W1≤0.5mm. The double-hole blade is installed in the accommodating area on the tool clamp, and the double-hole blade is limited by the locking front side and the blade limit platform. Due to the provision of the elastic groove, and W1<W2, 0.05mm≤W2-W1≤0.5mm, the tool clamp mounting part and the tool clamp locking part undergo elastic deformation to generate an elastic clamping force to lock the double-hole blade. The clamping force is large enough, and the clamping is stable and reliable. The tool clamp limiting hole and the stud screw accommodating groove are provided on the tool clamp to facilitate the installation and positioning of the tool clamp on the tool body.

[0019] (2) The turning tool of the present invention comprises a tool body, a double-hole blade, a limiting screw, a double-head screw and a tool holder for the above-mentioned double-hole blade. The double-hole blade is installed on the tool holder, and the two positioning holes are respectively matched with the two blade limiting platforms. The tool holder is installed in the tool groove of the tool body. A screw hole corresponding to the tool holder limiting hole is opened on the bottom surface of the tool groove, and a double-head screw hole corresponding to the double-head screw receiving groove is opened on the main side wall of the tool groove. The limiting screw passes through the tool holder limiting hole and matches with the screw hole. The two ends of the double-head screw respectively match with the double-head screw hole and the double-head screw receiving groove. The tool holder of the present invention clamps the double-hole blade and positions and locks the tool holder by the limiting screw and the double-head screw. The structure is compact and the clamping force is sufficient. The double-hole blade is not easy to loosen or fail due to insufficient clamping force during the cutting process. The processing quality is good and the tool life is long. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a three-dimensional structural diagram of the tool holder of the double-hole blade of the present invention.

[0021] Figure 2 It is a front view of the tool holder of the double-hole blade of the present invention when the double-hole blade is installed.

[0022] Figure 3 It is a side view of the tool holder of the double-hole blade of the present invention when the double-hole blade is installed.

[0023] Figure 4It is a three-dimensional structural diagram of the turning tool of the present invention.

[0024] Figure 5 It is a three-dimensional structural diagram of a double-hole blade of a turning tool of the present invention.

[0025] Figure 6 It is a three-dimensional structural diagram of the tool groove of the turning tool of the present invention.

[0026] Figure 7 It is a schematic diagram of the installation of the stud screw of the turning tool of the present invention.

[0027] The symbols in the figure represent:

[0028] 1. Tool holder installation part; 11. Install the upper surface; 12. Position the lower surface; 13. Install the front side; 14. Install the rear side; 15. Install the left side; 16. Install the right side; 17. Tool slot positioning part; 2. Tool holder locking part; 21. Lock the front side; 22. Lock the rear side; 23. Lock the left side; 24. Lock the right side; 3. Elastic groove; 4. Blade limiter; 41. Upper limiter; 42. Lower limiter; 5 , tool holder limiting hole; 6, stud screw receiving groove; 7, tool body; 71, limiting screw; 72, stud screw; 721, screw drive part; 722, screw neck; 723, screw limiting part; 73, locking screw; 8, double-hole blade; 81, positioning hole; 82, blade main side; 83, blade right side; 9, tool holder; 10, tool groove; 101, screw hole; 102, stud screw hole; 103, locking screw hole. DETAILED DESCRIPTION

[0029] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0030] Figures 1 to 3An embodiment of a tool holder for a double-hole blade of the present invention is shown, wherein the tool holder for the double-hole blade of this embodiment comprises an integrated tool holder mounting portion 1 and a tool holder locking portion 2, the mounting upper surface 11 of the tool holder mounting portion 1 intersects with the locking front side surface 21 of the tool holder locking portion 2 to form a receiving area for the double-hole blade 8, and an elastic groove 3 is provided at the intersection, the mounting upper surface 11 is provided with two blade limiting platforms 4 which are perpendicular to the mounting upper surface 11 and correspond to the two positioning holes 81 of the double-hole blade 8, the tool holder mounting portion 1 is provided with at least two tool holder limiting holes 5 which pass through its positioning lower surface 12 and the mounting upper surface 11, the locking rear side surface 22 of the tool holder locking portion 2 is provided with a stud screw receiving groove 6, the distance between the locking front side surface 21 and the proximal edge of the blade limiting platform 4 is W1, and the tool holder 8 which cooperates with the locking front side surface 21 is The distance between the main side surface 82 of the blade and the proximal edge of the positioning hole 81 of the double-hole blade 8 is W2, which should satisfy: W1<W2, 0.05mm≤W2-W1≤0.5mm. The double-hole blade 8 is installed in the accommodating area on the tool clamp, and the double-hole blade 8 is limited by the locking front side surface 21 and the blade limiting platform 4. Due to the provision of the elastic groove 3, and W1<W2, the tool clamp mounting portion 1 and the tool clamp locking portion 2 are elastically deformed to generate an elastic clamping force to lock the double-hole blade 8, satisfying 0.05mm≤W2-W1≤0.5mm, which not only ensures that the clamping force is large enough, the clamping is stable and reliable, but also facilitates the installation of the double-hole blade 8. The tool clamp limiting hole 5 and the stud screw accommodating groove 6 are provided on the tool clamp to facilitate the installation and positioning of the tool clamp on the tool. In this embodiment, W1=10mm, W2=10.2mm.

[0031] In this embodiment, the mounting upper surface 11 and the positioning lower surface 12, the mounting front side surface 13 and the mounting rear side surface 14, and the mounting left side surface 15 and the mounting right side surface 16 of the tool clamp mounting portion 1 are parallel to each other, the locking front side surface 21 and the locking rear side surface 22 of the tool clamp locking portion 2 are parallel to each other and perpendicular to the mounting upper surface 11, and the locking left side surface 23 and the locking right side surface 24 of the tool clamp locking portion 2 are parallel, which facilitates the installation and positioning of the tool clamp on the turning tool.

[0032] In this embodiment, the distances between the installation rear side surface 14, the locking front side surface 21, the locking rear side surface 22 and the installation front side surface 13 are L1, L2 and L3 respectively, and should satisfy: L2<L1<L3. There is a position difference between the installation rear side surface 14 and the locking rear side surface 22, and the positioning of the tool holder on the turning tool is more stable. By setting L2<L1<L3, the elastic locking of the double-hole blade 8 by the tool holder locking part 2 is more reliable.

[0033] In this embodiment, the distance between the locking left side 23 and the locking right side 24 is the same as the left and right length of the double-hole blade 8. The installation right side 16 is located to the right of the locking right side 24 so that a tool groove positioning portion 17 is formed on the right side of the tool clamp mounting portion 1. The tool groove positioning portion 17 further improves the stability of the tool clamp when installed on the turning tool.

[0034] In this embodiment, the blade limit platform 4 includes an upper limit portion 41 and a lower limit portion 42. The upper limit portion 41 and the lower limit portion 42 are both cylindrical and have diameters of d1 and d2 respectively. The diameter of the positioning hole 81 is D, which should satisfy: d2<d1<D. The height of the upper limit portion 41 is H, which should satisfy: 1mm≤H≤5mm. The force of the blade limit platform 4 on the positioning hole 81 of the double-hole blade 8 is mainly located at the upper limit portion 41, which improves the stability of clamping the double-hole blade 8. In this embodiment, D=6mm, d1=5.8mm, d2=5.5mm, and H=3mm.

[0035] Figures 4 to 7 An embodiment of the turning tool of the present invention is shown, and the turning tool of this embodiment includes a tool body 7, a double-hole blade 8, a limiting screw 71, a stud screw 72 and a tool holder 9 of the above-mentioned double-hole blade, the double-hole blade 8 is mounted on the tool holder 9, two positioning holes 81 are respectively matched with two blade limiting platforms 4, the tool holder 9 is mounted in the tool groove 10 of the tool body 7, a screw hole 101 corresponding to the tool holder limiting hole 5 is opened on the bottom surface of the tool groove 10, and a stud screw corresponding to the stud screw receiving groove 6 is opened on the main side wall of the tool groove 10 Screw hole 102, the limit screw 71 passes through the tool clamp limit hole 5 and cooperates with the screw hole 101, the two ends of the stud screw 72 respectively cooperate with the stud screw hole 102 and the stud screw accommodating groove 6, the double-hole blade 8 is installed in the above-mentioned tool clamp 9, the clamping of the double-hole blade 8 is stable and reliable, the tool clamp 9 is positioned and locked by the limit screw 71 and the stud screw 72, the structure is compact, the clamping force is sufficient, the double-hole blade 8 is not easy to loosen or fail due to insufficient clamping force during the cutting process, the processing quality is good and the tool life is long.

[0036] In this embodiment, the right side surface 83 of the double-hole blade 8 cooperates with the upper part of the right side wall of the knife groove 10, further improving the positioning stability and positioning accuracy of the double-hole blade 8. The center of the positioning hole 81 of the double-hole blade 8 and the center of the blade limit platform 4 have an eccentricity E in the direction perpendicular to the installation right side surface 16, which should satisfy: 0.05mm≤E≤0.5mm, further improving the clamping force of the tool clamp locking part 2 on the double-hole blade 8. The blade limit platform 4 has sufficient clamping force on the positioning hole 81 in the direction perpendicular to the installation right side surface 16, so that the right side surface 83 of the blade of the double-hole blade 8 is tightly pressed with the upper part of the right side wall of the knife groove 10.

[0037] In this embodiment, the positioning lower surface 12 of the tool clamp 9 cooperates with the bottom surface of the tool groove 10, the locking rear side surface 22 of the tool clamp 9 cooperates with the gap between the upper main side wall of the tool groove 10, the installation rear side surface 14 of the tool clamp cooperates with the lower main side wall of the tool groove 10, the lower part of the right side wall of the tool groove 10 is recessed to the right to form a positioning groove, the tool groove positioning portion 17 cooperates with the positioning groove, and the tool groove realizes positioning and clamping of the tool clamp 9 through the cooperation of multiple areas such as the bottom surface, the upper main side wall, the lower main side wall, and the positioning groove, and the structure is stable and reliable.

[0038] In this embodiment, two locking screw holes 103 are further provided on the main side wall of the knife groove 10, and the two locking screws 73 are respectively installed in the locking screw holes 103 and the ends are in contact with the locking rear side surface 22. By the locking screws 73 acting on the locking rear side surface 22, the locking front side surface 21 can be tightly fitted to the double-hole blade, thereby further locking the double-hole blade 8.

[0039] In this embodiment, the double-headed screw 72 includes a screw driving part 721, a screw neck 722 and a screw limiting part 723 in sequence. The double-headed screw receiving groove 6 also includes a neck cavity 61. The screw limiting part 723 is installed in the double-headed screw receiving groove 6. The screw driving part 721 is provided with an external thread and cooperates with the double-headed screw hole 102. The screw neck 722 is located in the neck cavity 61. The diameters of the screw driving part 721, the screw neck 722 and the screw limiting part 723 are D1, D2 and D3 respectively. The diameter of the neck cavity 61 is dx, which should satisfy: D2<D1, D2<D3, D2<dx<D3. The screw neck 722 and the neck cavity 61, the screw limiting part 723 and the double-headed screw receiving groove 6 are all clearance fit. The double-headed screw 72 can not only lock the tool clamp 9, but also control the tool clamp locking part 2 to produce elastic deformation to achieve a certain degree of opening, so as to facilitate the double-hole blade 8 to be installed in the tool clamp 9.

[0040] In this embodiment, an operating tool clamping portion is provided at the end of the screw driving portion 721 to facilitate installation.

[0041] The front, back, left, right, top, bottom, etc. described in the present invention are all based on the placement of the tool as shown in the accompanying drawings for ease of understanding.

[0042] Although the present invention has been disclosed as above with preferred embodiments, it is not intended to limit the present invention. Any technician familiar with the art can make many possible changes and modifications to the technical solution of the present invention by using the technical content disclosed above without departing from the scope of the technical solution of the present invention, or modify it into an equivalent embodiment of equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention should fall within the scope of protection of the technical solution of the present invention.

Claims

1. A tool holder for a double-hole blade, characterized in that: The invention comprises an integrated knife clamp mounting portion (1) and a knife clamp locking portion (2), wherein the mounting upper surface (11) of the knife clamp mounting portion (1) intersects with the locking front side surface (21) of the knife clamp locking portion (2) to form a receiving area for a double-hole blade (8), and an elastic groove (3) is provided at the intersection, and two blade stop platforms (4) perpendicular to the mounting upper surface (11) and corresponding to two positioning holes (81) of the double-hole blade (8) are provided on the mounting upper surface (11), and at least two positioning lower surfaces (21) are provided on the knife clamp mounting portion (1) to penetrate the positioning lower surface (21). (12) and a tool holder limiting hole (5) on the mounting upper surface (11), a double-headed screw receiving groove (6) is provided on the locking rear side surface (22) of the tool holder locking portion (2), the distance between the locking front side surface (21) and the proximal edge of the blade limiting platform (4) is W1, and the distance between the blade main side surface (82) of the double-hole blade (8) that cooperates with the locking front side surface (21) and the proximal edge of the positioning hole (81) of the double-hole blade (8) is W2, which should satisfy: W1<W2, 0.05mm≤W2-W1≤0.5mm.

2. The tool holder for a double-hole blade according to claim 1, characterized in that: The mounting upper surface (11) and the positioning lower surface (12), the mounting front side surface (13) and the mounting rear side surface (14), the mounting left side surface (15) and the mounting right side surface (16) of the tool clamp mounting portion (1) are parallel to each other; the locking front side surface (21) and the locking rear side surface (22) of the tool clamp locking portion (2) are parallel to each other and perpendicular to the mounting upper surface (11); the locking left side surface (23) and the locking right side surface (24) of the tool clamp locking portion (2) are parallel to each other.

3. The tool holder for a double-hole blade according to claim 2, characterized in that: The distances between the installation rear side surface (14), the locking front side surface (21), the locking rear side surface (22) and the installation front side surface (13) are L1, L2 and L3 respectively, and should satisfy the following: L2<L1<L3.

4. The tool holder for a double-hole blade according to claim 2, characterized in that: The distance between the locking left side surface (23) and the locking right side surface (24) is the same as the left-right length of the double-hole blade (8), and the mounting right side surface (16) is located to the right of the locking right side surface (24) so ​​that a knife groove positioning portion (17) is formed on the right side of the knife clamp mounting portion (1).

5. The tool holder for a double-hole blade according to claim 1, characterized in that: The blade limiting platform (4) comprises an upper limiting portion (41) and a lower limiting portion (42); the upper limiting portion (41) and the lower limiting portion (42) are both cylindrical and have diameters d1 and d2 respectively; the diameter of the positioning hole (81) is D and should satisfy: d2<d1<D; the height of the upper limiting portion (41) is H and should satisfy: 1mm≤H≤5mm.

6. A turning tool, characterized in that: A tool holder (9) comprising a tool body (7), a double-hole blade (8), a limiting screw (71), a stud screw (72) and a double-hole blade according to any one of claims 1 to 5, wherein the double-hole blade (8) is mounted on the tool holder (9), the two positioning holes (81) respectively cooperate with the two blade limiting platforms (4), the tool holder (9) is mounted in a tool groove (10) of the tool body (7), a screw hole (101) corresponding to the tool holder limiting hole (5) is provided on the bottom surface of the tool groove (10), a stud screw hole (102) corresponding to the stud screw receiving groove (6) is provided on the main side wall of the tool groove (10), the limiting screw (71) passes through the tool holder limiting hole (5) and cooperates with the screw hole (101), and two ends of the stud screw (72) respectively cooperate with the stud screw hole (102) and the stud screw receiving groove (6).

7. The turning tool according to claim 6, characterized in that: The installation upper surface (11) and the positioning lower surface (12), the installation front side surface (13) and the installation rear side surface (14), the installation left side surface (15) and the installation right side surface (16) of the tool clamp installation part (1) are parallel to each other, the locking front side surface (21) and the locking rear side surface (22) of the tool clamp locking part (2) are parallel to each other and perpendicular to the installation upper surface (11), the locking left side surface (23) and the locking right side surface (24) of the tool clamp locking part (2) are parallel, the blade right side surface (83) of the double-hole blade (8) cooperates with the upper part of the right side wall of the knife groove (10), the center of the positioning hole (81) of the double-hole blade (8) and the center of the blade limit platform (4) have an eccentricity E in a direction perpendicular to the installation right side surface (16), which should satisfy: 0.05mm≤E≤0.5mm.

8. The turning tool according to claim 7, characterized in that: The positioning lower surface (12) of the tool clamp (9) cooperates with the bottom surface of the tool groove (10), the locking rear side surface (22) of the tool clamp (9) cooperates with the upper part of the main side wall of the tool groove (10), the installation rear side surface (14) of the tool clamp cooperates with the lower part of the main side wall of the tool groove (10), the lower part of the right side wall of the tool groove (10) is recessed to the right to form a positioning groove, the installation right side surface (16) is located on the right side of the locking right side surface (24) so ​​that the right side of the tool clamp installation part (1) forms a tool groove positioning part (17), and the tool groove positioning part (17) cooperates with the positioning groove.

9. The turning tool according to any one of claims 6 to 8, characterized in that: Two locking screw holes (103) are also provided on the main side wall of the knife groove (10), and two locking screws (73) are respectively installed in the locking screw holes (103) with their ends in contact with the locking rear side surface (22).

10. The turning tool according to any one of claims 6 to 8, characterized in that: The stud screw (72) comprises a screw driving portion (721), a screw neck (722) and a screw limiting portion (723) in sequence; the stud screw receiving groove (6) further comprises a neck cavity (61); the screw limiting portion (723) is installed in the stud screw receiving groove (6); the screw driving portion (721) is provided with an external thread and cooperates with the stud screw hole (102); the screw neck (722) is located in the neck cavity (61); the diameters of the screw driving portion (721), the screw neck (722) and the screw limiting portion (723) are D1, D2 and D3 respectively; the diameter of the neck cavity (61) is dx, which should satisfy the following conditions: D2<D1, D2<D3, D2<dx<D3.

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