CN213764890U

CN213764890U - Adjustable positioning fixture

Info

Publication number: CN213764890U
Application number: CN202021957929.0U
Authority: CN
Inventors: 刘勇; 刘志敏
Original assignee: HUBEI SHENLI FORGING CO Ltd
Current assignee: HUBEI SHENLI FORGING CO Ltd
Priority date: 2020-09-09
Filing date: 2020-09-09
Publication date: 2021-07-23
Anticipated expiration: 2030-09-09

Abstract

The utility model provides a positioning fixture with adjustable, include: the clamp comprises a clamp body, wherein a waist-shaped groove is arranged on the surface of the clamp body in the transverse direction; the positioning panel is arranged on the surface of the clamp body, the positioning panel can move relative to the clamp body along the length direction of the waist-shaped groove, bolt holes are formed in the positioning panel, a locking assembly is arranged between the bolt holes and the waist-shaped groove, one surface, far away from the clamp body, of the positioning panel is provided with an installing cavity with an opening at the top, a sliding block is arranged in the installing cavity in a sliding mode, threaded holes communicated with the installing cavity are formed in the upper side wall and the lower side wall of the positioning panel respectively, a first bolt is connected to each threaded hole, and the end portion of the first bolt is abutted to the sliding block. The utility model discloses a positioning fixture can realize treating the horizontal, the vertical direction of processing part to have the adjustment of poor utmost point through utilizing locking Assembly and first bolt, and the flexibility is high, the location requirement of adaptable multiple part, can be unanimous with the reference position adjustment of front and back process during the remodeling, guarantees its uniformity to reach the purpose of remodeling fast.

Description

Adjustable positioning fixture

Technical Field

The utility model relates to a parts machining technology field especially relates to a positioning fixture with adjustable.

Background

For part processing, particularly for a flow production line, the processing of each process needs to adopt the positioning action of a clamp to ensure the relative position of a workpiece, wherein the positioning mode of 'one surface and two pins' is one of the most common modes, and because the factors of clamping, interchangeability, positioning hole processing precision and the like are considered, the gap amount between a positioning pin and a positioning hole cannot be too small, so that under the condition that long parts are processed and the positioning hole cannot be designed to two ends, the positioning error caused by the gap is amplified, the positioning references of the front process and the rear process are inaccurate and inconsistent, the error of a conventional positioning clamp is difficult to eliminate, and the processing quality cannot be ensured, for example, the phenomena of hole drilling deviation, hole expanding non-concentricity, insufficient wall thickness, ultra-poor milling position and the like exist.

Meanwhile, considering that various types of the clamp still need to have flexibility, the design of the clamp is more important.

SUMMERY OF THE UTILITY MODEL

In view of this, the utility model provides a positioning fixture with adjustable can realize the equal adjustable function in vertical and horizontal direction, can be unanimous with the reference position adjustment of front and back process during the remodeling, guarantees its uniformity to reach the purpose of remodeling fast.

The technical scheme of the utility model is realized like this: the utility model provides a positioning fixture with adjustable, include:

the clamp comprises a clamp body, wherein two waist-shaped grooves which are parallel to each other and run through the clamp body are arranged on the surface of the clamp body in the transverse direction;

the positioning panel is arranged on the surface of the clamp body and can move relative to the clamp body along the length direction of the waist-shaped groove, a bolt hole communicated with the waist-shaped groove is formed in the positioning panel, an installation cavity with an opening at the top is formed in one surface, away from the clamp body, of the positioning panel, and threaded holes communicated with the installation cavity are formed in the upper side wall and the lower side wall of the positioning panel respectively;

the locking assembly is arranged between the bolt hole and the waist-shaped groove and is used for adjusting and locking the position of the positioning panel and the clamp body in the transverse direction;

the sliding block is arranged in the mounting cavity and can move along the longitudinal direction of the mounting cavity, and a plurality of positioning holes for connecting positioning pins are formed in the top surface of the sliding block;

and the end part of the first bolt is abutted against the sliding block and is used for adjusting and locking the position of the sliding block and the positioning panel in the longitudinal direction.

On the basis of the technical scheme, preferably, at least one bolt hole is formed in the surface of the positioning panel corresponding to each waist-shaped groove.

Furthermore, the locking assembly comprises a second bolt and a nut, and the second bolt penetrates through the bolt hole and the waist-shaped groove and is connected with the nut.

On the basis of the technical scheme, preferably, the mounting cavity comprises a first cavity and a second cavity which are communicated with each other, the first cavity is located on one surface, away from the clamp body, of the positioning panel, the second cavity is arranged in the positioning panel on which one side of the first cavity is located, the threaded hole is communicated with the second cavity, the width of the first cavity in the longitudinal direction is smaller than that of the second cavity, the sliding block comprises a first sliding portion and a second sliding portion, and the width of the second sliding portion in the longitudinal direction is smaller than that of the first sliding portion; the first sliding portion is inserted in the second cavity, the second sliding portion is inserted in the first cavity, the width of the first sliding portion in the longitudinal direction is smaller than that of the second cavity, and the width of the second sliding portion in the longitudinal direction is smaller than that of the first cavity.

Furthermore, the second cavity extends to the surface of the positioning panel, which is in contact with the clamp body, and is in an opening shape, and the side surface of the second sliding part is flush with the surface of the clamp body.

Furthermore, the top surface of the first sliding part is flush with one surface, away from the clamp body, of the positioning panel, and the positioning holes are formed in the top surface of the first sliding part at equal intervals along the length direction of the sliding block.

On the basis of the above technical scheme, preferably, at least one threaded hole is respectively arranged on the upper side wall and the lower side wall of the positioning panel, and the threaded holes on the upper side wall and the lower side wall of the positioning panel are aligned with each other in the longitudinal direction.

On the basis of the technical scheme, preferably, two fixture body surfaces in the middle of the waist-shaped grooves are provided with guide grooves, the guide key grooves are parallel to the waist-shaped grooves, and the bottom of the positioning panel is provided with guide keys matched with the guide grooves in a sliding mode.

Preferably, the first bolt and the second bolt are both hexagon socket head cap bolts.

The utility model discloses following beneficial effect has for prior art:

the utility model discloses a positioning fixture with adjustable, can be in lathe both sides symmetrical arrangement, when fixing a position the clamping to the part, at first through the positioning fixture of lathe one side, align the locating hole of part one end and the locating hole on the slider and use the locating pin to fix, the one end that makes the part is as the initial positioning benchmark, utilize locking Assembly and first bolt can adjust the slider on the lathe opposite side positioning fixture respectively for the locating hole of the part other end horizontal, the ascending position of vertical side, thereby guarantee the part other end accurate positioning on the positioning fixture of lathe opposite side. When the clamping is replaced for the similar products with different length models, the center distance of the positioning holes is not consistent, so that the former initial positioning reference is only needed to be used, and then the other end of the part is adjusted to be clamped on the positioning clamp. Therefore, the reference positions of the front and rear processes can be adjusted consistently during model changing, the consistency of the reference positions is guaranteed, and the purpose of rapid model changing is achieved. Compared with the prior art, the clamp has the advantages that the locking assembly and the first bolt are utilized to respectively realize the adjustment of the part to be machined in the transverse direction and the longitudinal direction of the clamp body, the flexibility is high, the clamp can meet the positioning requirements of various parts, the reference positions of the front working procedure and the rear working procedure can be adjusted consistently during the model changing process, the consistency of the reference positions is guaranteed, and the purpose of rapid model changing is achieved.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

FIG. 1 is a schematic view of a positioning fixture disclosed in the prior art;

fig. 2 is a schematic plan view of the adjustable positioning fixture of the present invention;

fig. 3 is a schematic side view of the adjustable positioning fixture of the present invention;

fig. 4 is a schematic view of an assembly structure of the top panel and the slider according to the present invention;

fig. 5 is a state diagram of the adjustable positioning fixture of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments in the present invention, all other embodiments obtained by a person skilled in the art without creative work all belong to the protection scope of the present invention.

As shown in fig. 1, a positioning fixture adopted in the prior art mainly adopts a fixture body 1, a positioning panel 2 and a positioning pin 6, such a positioning fixture can only be suitable for clamping a part with a determined positioning hole center distance, and when an error occurs in a part positioning hole in a machining process, the part cannot be clamped by the existing positioning fixture.

From this, as shown with reference to fig. 2 and 3, the embodiment of the present invention discloses an adjustable positioning fixture, and this positioning fixture 100 includes fixture body 1, positioning panel 2, locking component 3, slider 4 and first bolt 5.

The fixture body 1 is configured to be mounted on a machine tool 200, in this embodiment, the fixture body 1 is a rectangular plate-shaped structure, two waist-shaped grooves 11 that are parallel to each other are arranged in a transverse direction on a surface of the fixture body 1, the two waist-shaped grooves 11 are symmetrically arranged along a transverse central cross section of the fixture body 1, and the waist-shaped grooves 11 penetrate through upper and lower surfaces of the fixture body 1.

Positioning panel 2 sets up on anchor clamps body 1 surface, can follow waist type groove 11 length direction and remove for anchor clamps body 1, is provided with the bolt hole 21 that is linked together with waist type groove 11 on positioning panel 2, and open-top's installation cavity 22 is seted up to the one side that positioning panel 2 kept away from anchor clamps body 1, sets up the screw hole 23 that is linked together with installation cavity 22 on positioning panel 2's the upper and lower lateral wall respectively.

And the locking assembly 3 is arranged between the bolt hole 21 and the waist-shaped groove 11 and is used for adjusting and locking the position of the positioning panel 2 and the clamp body 1 in the transverse direction.

The sliding block 4 is arranged in the installation cavity 22 and can move along the longitudinal direction of the installation cavity 22, a plurality of positioning holes 41 used for connecting positioning pins are formed in the top surface of the sliding block 4, and when parts are clamped, the positioning holes 41 in the parts are aligned to the positioning holes 41 in the sliding block 4, and then the positioning pins 6 are inserted into the positioning holes 41 for transitional connection.

And the first bolt 5 is in threaded connection with the threaded hole 23, and the end part of the first bolt 5 is abutted against the sliding block 4 for adjusting and locking the position of the sliding block 4 and the positioning panel 2 in the longitudinal direction.

Adopt above-mentioned technical scheme, the utility model discloses a positioning fixture with adjustable, can be at lathe 200 bilateral symmetry arrangement, when fixing a position the clamping to part 300, the locating hole 41 centre-to-centre spacing at part 300 both ends is known, at first positioning fixture 100 through lathe 200 one side, align the locating hole 41 of part 300 one end and the locating hole on slider 4 and use locating pin 6 to fix, make the one end of part 300 as the initial positioning benchmark, it is horizontal for the locating hole of the part 300 other end to utilize locking Assembly 3 and first bolt 5 can adjust slider 4 on lathe 200 opposite side positioning fixture 100 respectively, the ascending position of longitudinal direction, thereby guarantee that the part 300 other end is accurate location on the positioning fixture 100 of lathe 200 opposite side. When the clamping of the similar products is replaced with different length models, the center distance of the positioning holes of the part 300 is not consistent, and only the previous initial positioning reference is used, and then the clamping position of the other end of the part 300 on the positioning clamp 100 is adjusted. Therefore, the reference positions of the front and rear processes can be adjusted consistently during model changing, the consistency of the reference positions is guaranteed, and the purpose of rapid model changing is achieved. Compared with the prior art, the locking assembly 3 and the first bolt 5 can be used for realizing the non-differential adjustment of the part 300 to be processed in the transverse and longitudinal directions of the clamp body 1, and the flexibility is high, so that the clamp can meet the positioning requirements of various parts 300. And the cost is low, the processed parts are fast to change the model, the adjustment is convenient, and the processing quality is more stable. The reference positions of the front and the rear working procedures can be adjusted to be consistent during model changing, and the consistency of the reference positions is ensured, so that the purpose of rapid model changing is achieved.

Specifically, the utility model discloses still realize through following technical scheme.

In some preferred embodiments, the surface of the positioning panel 2 corresponding to each of the waist-shaped grooves 11 is provided with at least one bolt hole 21. Therefore, the upper side and the lower side of the surface of the positioning panel 2 are respectively arranged in the bolt hole 21 and the corresponding waist-shaped groove 11 through one locking assembly 3, so that the positioning panel 2 and the clamp body 1 can be locked up and down. In order to improve the locking force between the positioning panel 2 and the fixture body 1, the surface of the positioning panel 2 corresponding to each of the waist-shaped grooves 11 may be provided with two or more bolt holes 21, so that the positioning panel 2 and the fixture body 1 are locked by more locking assemblies 3, and thus the locking force is better. As the utility model discloses a, four edges of positioning panel 2 all set up a bolt hole 21, from this for this positioning fixture 100 simple structure, low cost, and can realize stronger locking force.

As a preferred embodiment of the present invention, the locking assembly 3 includes a second bolt 31 and a nut 32, and the second bolt 31 passes through the bolt hole 21 and the kidney groove 11 and is connected to the nut 32. Therefore, when the transverse direction flexibility adjustment of the part 300 on the positioning clamp 100 needs to be realized, the positioning panel 2 is slid by loosening the connection force of the nut 32 and the second bolt 31, the positioning panel 2 and the locking assembly 3 move along the length direction of the waist-shaped groove 11, and after the proper position of the movement is reached, the nut 32 and the second bolt 31 are sufficiently locked, so that the relative position of the positioning panel 2 and the clamp body 1 can be fixed.

Referring to fig. 3 and 4, in the present embodiment, the mounting cavity 22 includes a first cavity 221 and a second cavity 222 which are communicated with each other, the first cavity 221 is located on a surface of the positioning panel 2 away from the clamp body 1, the second cavity 222 is disposed in the positioning panel 2 on a side of the first cavity 221, the threaded hole 23 is communicated with the second cavity 222, a width of the first cavity 221 in the longitudinal direction is smaller than a width of the second cavity 222, the slider 4 includes a first sliding portion 42 and a second sliding portion 43, and a width of the second sliding portion in the longitudinal direction is smaller than a width of the first sliding portion; the first sliding portion 42 is inserted in the second chamber 222, the second sliding portion 43 is inserted in the first chamber 221, the width of the first sliding portion 42 in the longitudinal direction is smaller than the width of the second chamber 222, and the width of the second sliding portion 43 in the longitudinal direction is smaller than the width of the first chamber 221.

With the above technical solution, the width of the first cavity 221 in the longitudinal direction is smaller than the width of the second cavity 222, and the width of the second sliding portion 43 in the longitudinal direction is smaller than the width of the first sliding portion 42, so that the second sliding portion 43 can be clamped in the first cavity 221, and the first sliding portion 42 cannot move in the first cavity 221. By the width of the first sliding portion 42 in the longitudinal direction being smaller than the width of the second chamber 222 and the width of the second sliding portion 43 in the longitudinal direction being smaller than the width of the first chamber 221, the first sliding portion 42 can slide in the longitudinal direction in the second chamber 222 and the second sliding portion 43 can slide in the longitudinal direction in the first chamber 221. The first bolt 5 is in threaded connection with the threaded hole 23, the end of the first bolt 5 is abutted against the second sliding portion 43 in the second chamber 222, and by rotating the first bolt 5, the first bolt 5 pushes the second sliding portion 43, so that the first sliding portion 42 moves in the second chamber 222 along the longitudinal direction, the slider 4 is adjusted in the longitudinal direction, and finally the part 300 is flexibly adjusted in the longitudinal direction on the positioning fixture 100.

As a further improvement of the above embodiment, the second cavity 222 extends to the surface of the positioning panel 2 contacting the clamp body 1, and is open, and the side surface of the second sliding portion 43 is flush with the surface of the clamp body 1. By adopting the technical scheme, the second cavity 222 and the first cavity 221 are communicated with each other, and the formed mounting cavity 22 penetrates through the positioning panel 2, so that the sliding block 4 is conveniently mounted in the mounting cavity 22 of the positioning panel 2 from the second cavity 222, and is also convenient to detach, repair or replace.

On the basis of above-mentioned embodiment, the one side that anchor clamps body 1 was kept away from to first sliding part 42 top surface and location panel 2 flushes mutually, therefore, can be convenient when part 300 and slider 4 are installed fixedly, part 300 can be fine laminate with slider 4 top surface, a plurality of locating holes 41 set up the top surface at first sliding part 42 along slider 4's length direction equidistant, equidistant a plurality of locating holes 41 that set up, can conveniently carry out the clamping location to the part 300 of different length, the different diameters of different diameters can be designed as required in the aperture of a plurality of locating holes 41 simultaneously, with the diameter of adaptation part 300 locating hole 41. When fixing the part 300 and the slider 4, the positioning hole 41 of the part 300 is first aligned with the positioning hole 41 of the slider 4, and then the positioning pin 6 is inserted for transition fit.

As some embodiments of the utility model, be provided with at least one screw hole 23 on the upper and lower lateral wall of positioning panel 2 respectively, and screw hole 23 on the lateral wall aligns each other in longitudinal direction about positioning panel 2. Because the first sliding portion 42 is in clearance fit in the longitudinal direction of the first cavity 221, and the second sliding portion 43 is also in clearance fit in the longitudinal direction of the second cavity 222, the second sliding portion 43 can keep the transverse direction from rotating under the action of the upper and lower abutting forces by abutting the first bolt 5 on the upper and lower sides of the second sliding portion, but in order to avoid the slider 4 from rotating in the transverse direction, when the two threaded holes 23 are respectively formed in the upper and lower side walls of the positioning panel 2, the second sliding portion 43 can have two abutting forces on the upper and lower sides, so that the problem that the slider 4 rotates under the condition that only one abutting force exists on the upper and lower sides can be completely avoided.

As the preferred embodiment of the utility model, the surface of the fixture body 1 in the middle of the waist-shaped groove 11 is provided with the guide groove 12, the guide key groove is parallel to the waist-shaped groove 11, and the bottom of the positioning panel 2 is provided with the guide key 24 which is matched with the guide groove 12 for sliding. By adopting the technical scheme, when the positioning panel 2 moves along the transverse direction of the clamp body 1, the positioning panel can be guided to move in the guide groove 12 through the guide key 24, so that the situation that the positioning panel 2 moves and deviates when moving and adjusting in the transverse direction is avoided. Preferably, the guide keys 24 are fixed to the bottom of the positioning panel 2 at both sides of the slider 4 in the transverse direction, and the guide keys 24 may be fastened to the top panel by bolts.

In the present embodiment, the first bolt 5 and the second bolt 31 are both hexagon socket bolts. Therefore, the adjustment is convenient.

Referring to the attached drawings 2-5, the working principle of the utility model is as follows:

will the utility model discloses a 100 symmetry of positioning fixture are installed on lathe 200, guarantee simultaneously that two sets of positioning fixture 100 are in on same horizontal plane, and keep being parallel to each other. The part 300 to be machined needs to be clamped and positioned on the left positioning fixture 100 and the right positioning fixture 100, a positioning hole at one end of the part 300 is aligned with a positioning hole 41 on the sliding block 4 of the left positioning fixture 100, and then the part is fixed through a positioning pin 6, so that one end of the part 300 is fixed on the left positioning fixture 100 and is used as an initial positioning reference, and the central line of the part 300 is flush with the central connecting line of the two positioning fixtures 100. The other end of the part 300 is located on the right positioning fixture 100, and the position of the positioning hole 41 of the sliding block 4 relative to the positioning hole at the other end of the part 300 in the transverse direction is adjusted by adjusting the position of the positioning panel 2 on the right positioning fixture 100 relative to the transverse direction of the fixture body 1, so that the relative position of the positioning panel 2 and the fixture body 1 can be fixed through the locking assembly 3. When the positioning hole 41 at the other end of the part 300 is not located on the center line of the part 300 due to a machining precision error, that is, when the two sides of the center line of the part 300 are deviated, the amount of movement of the slider 4 in the longitudinal direction in the mounting cavity 22 is adjusted by the first bolt 5, so that the positioning hole 41 on the slider 4 is overlapped with the positioning hole 41 at the other end of the part 300, after the overlapping, the positioning hole at the other end of the part 300 is connected with the positioning hole 41 on the slider 4 by the positioning pin 6, and further, the accurate positioning of the two ends of the part 300 is realized, because the two positioning holes on the part 300 are symmetrical with respect to the center of the part 300, after the part 300 is clamped and positioned on the positioning fixtures 100 at the left and right sides, the accurate machining of the machining parts at the two ends of the part 300 on the machine tool 200 can be realized.

The above description is only a preferred embodiment of the present invention, and should not be taken as limiting the invention, and any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An adjustable positioning fixture, comprising:

the clamp comprises a clamp body (1), wherein two waist-shaped grooves (11) which are parallel to each other and penetrate through the clamp body (1) are arranged on the surface of the clamp body (1) in the transverse direction;

the positioning panel (2) is arranged on the surface of the clamp body (1) and can move relative to the clamp body (1) along the length direction of the waist-shaped groove (11), a bolt hole (21) communicated with the waist-shaped groove (11) is formed in the positioning panel (2), an installation cavity (22) with an opening at the top is formed in one surface, away from the clamp body (1), of the positioning panel (2), and threaded holes (23) communicated with the installation cavity (22) are formed in the upper side wall and the lower side wall of the positioning panel (2) respectively;

the locking assembly (3) is arranged between the bolt hole (21) and the waist-shaped groove (11) and is used for adjusting and locking the position of the positioning panel (2) and the clamp body (1) in the transverse direction;

the sliding block (4) is arranged in the mounting cavity (22) and can move along the longitudinal direction of the mounting cavity (22), and a plurality of positioning holes (41) used for connecting positioning pins are formed in the top surface of the sliding block (4);

and the first bolt (5) is in threaded connection with the threaded hole (23), and the end part of the first bolt (5) is abutted to the sliding block (4) and used for adjusting and locking the position of the sliding block (4) and the positioning panel (2) in the longitudinal direction.

2. The adjustable positioning fixture of claim 1, wherein: each positioning panel (2) corresponding to the waist-shaped groove (11) is provided with at least one bolt hole (21).

3. The adjustable positioning fixture of claim 2, wherein: the locking assembly (3) comprises a second bolt (31) and a nut (32), and the second bolt (31) penetrates through the bolt hole (21) and the waist-shaped groove (11) and is connected with the nut (32).

4. The adjustable positioning fixture of claim 1, wherein: the mounting cavity (22) comprises a first cavity (221) and a second cavity (222) which are communicated with each other, the first cavity (221) is located on one surface, away from the clamp body (1), of the positioning panel (2), the second cavity (222) is arranged in the positioning panel (2) where one side of the first cavity (221) is located, the threaded hole (23) is communicated with the second cavity (222), the width of the first cavity (221) in the longitudinal direction is smaller than that of the second cavity (222), the sliding block (4) comprises a first sliding portion (42) and a second sliding portion (43), and the width of the second sliding portion (43) in the longitudinal direction is smaller than that of the first sliding portion (42); the first sliding portion (42) is inserted into the second chamber (222), the second sliding portion (43) is inserted into the first chamber (221), the width of the first sliding portion (42) in the longitudinal direction is smaller than the width of the second chamber (222), and the width of the second sliding portion (43) in the longitudinal direction is smaller than the width of the first chamber (221).

5. The adjustable positioning fixture of claim 4, wherein: the second cavity (222) extends to the surface of the positioning panel (2) contacted with the clamp body (1) and is in an opening shape, and the side surface of the second sliding part (43) is flush with the surface of the clamp body (1).

6. The adjustable positioning fixture of claim 5, wherein: the top surface of the first sliding portion (42) is flush with one surface, away from the clamp body (1), of the positioning panel (2), and the positioning holes (41) are arranged on the top surface of the first sliding portion (42) at equal intervals along the length direction of the sliding block (4).

7. The adjustable positioning fixture of claim 1, wherein: the upper side wall and the lower side wall of the positioning panel (2) are respectively provided with at least one threaded hole (23), and the threaded holes (23) in the upper side wall and the lower side wall of the positioning panel (2) are aligned with each other in the longitudinal direction.

8. The adjustable positioning fixture of claim 1, wherein: two anchor clamps body (1) surface at place in the middle of waist type groove (11) is provided with guide way (12), guide way (12) are parallel with waist type groove (11), locating panel (2) bottom is provided with and cooperates gliding guide key (24) with guide way (12).

9. The adjustable positioning fixture of claim 3, wherein: the first bolt (5) and the second bolt (31) are both hexagon socket head cap bolts.