A limit-avoidance composite positioning fixture
Patent Information
- Application Number
- CN202522276819.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-27
- Publication Date
- 2026-09-01
- Estimated Expiration
- 2035-10-27
AI Technical Summary
[0004]传统治具缺乏对中心导体与铁氧体两者之间相对位置的精密约束结构，无法有效管控两者的同轴精度，这直接影响其组装后的结构稳定性
本实用新型提供的限位避让式复合定位治具，通过上限位片的放置贯穿孔与下限位片的底部中心孔采用同轴设置，为中心导体与铁氧体的组装提供了明确且统一的同轴基准；上限位片的多个分支长孔绕放置中心孔周向分布且与中心导体各悬臂端一一对应，下限位片底部中心孔周向内侧壁的多个避让孔也与中心导体各悬臂端一一对应，这种对应结构既实现了对中心导体悬臂端的精准避让（避免传统治具挤压悬臂端引发的变形或应力集中），又能通过分支长孔与避让孔的周向限位作用，防止中心导体组装过程中发生周向旋转，保障中心导体与铁氧体的角度精度；再者，下限位片底部中心孔的深度大于中心导体的中部厚度，可对中心导体中部形成适配的容纳空间，配合上限位片对中心导体上部的限位，从上下方向约束中心导体的径向窜动，进一步提升相对位置稳定性；最后，底座上对应底部中心孔位置设置的真空气孔，能通过真空吸附作用增强铁氧体与中心导体在组装过程中的位置固定效果，减少组装过程中的移位风险，最终通过上述上限位片、下限位片与底座的结构协同，形成对中心导体与铁氧体相对位置的全维度精密约束，有效管控两者的同轴精度，提升环形器/隔离器组装后的结构稳定性。
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Figure CN224708960U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to the field of tooling and fixture technology, and in particular to a limit-avoidance composite positioning fixture. Background Technology
[0002] Circulators / isolators are indispensable passive components in radio frequency and microwave systems, and are widely used in radar, communication systems, test instruments, medical equipment, etc.
[0003] The core structure of a circulator / isolator consists of a center conductor and a ferrite core. The performance of a circulator / isolator is highly dependent on the geometric accuracy between the center conductor and the ferrite core. The center conductor must maintain high-precision coaxiality with the cylindrical ferrite core. The angular accuracy of the center conductor and ferrite core after assembly is a key factor determining the final performance and reliability of the device.
[0004] Traditional fixtures lack a precise constraint structure for the relative position between the center conductor and the ferrite, making it impossible to effectively control the coaxial accuracy of the two, which directly affects the structural stability after assembly. Utility Model Content
[0005] The purpose of this invention is to provide a limit-avoidance composite positioning fixture to solve the problems existing in the prior art, improve the coaxial installation accuracy, and improve the stability of the assembly structure.
[0006] To achieve the above objectives, this utility model provides the following solution: This utility model provides a limit-and-avoidance composite positioning fixture, comprising an upper limit plate, a lower limit plate, and a base fixedly arranged from top to bottom; the upper limit plate has a through hole extending vertically, the through hole including a central hole and multiple branch elongated holes; each branch elongated hole is circumferentially distributed around the axis of the central hole, and each branch elongated hole corresponds to a cantilever end of a central conductor; the lower limit plate has a through hole extending vertically to the bottom, the depth of which is greater than the thickness of the middle part of the central conductor in the vertical direction; the bottom center hole is coaxially arranged with the central hole; multiple avoidance holes are formed on the inner circumferential sidewall of the bottom center hole, and each avoidance hole corresponds to a cantilever end of the central conductor; both the upper limit plate and the lower limit plate are fixedly arranged on the base, and the base has vacuum holes at positions corresponding to the bottom center hole.
[0007] Preferably, the placement through hole further includes multiple branch short holes; each of the branch short holes is circumferentially distributed around the axis of the placement center hole, and the branch short holes and the branch long holes are arranged opposite each other on both sides of the placement center hole; the branch short holes and the branch long holes are arranged directly opposite each other, the width of the branch long holes matches the maximum width of the cantilever end of the center conductor, and the width of the branch short holes matches the end width of the cantilever end of the center conductor.
[0008] Preferably, in the vertical direction, the upper limit plate and the lower limit plate have the same external dimensions, and the external dimensions of the base are larger than those of the lower limit plate; both the upper limit plate and the lower limit plate are detachably fixed on the base.
[0009] Preferably, the upper limit plate has two first mounting hole groups, each including multiple first fixing holes; the two first mounting hole groups are respectively arranged opposite to each other on both sides of the through hole; the lower limit plate has two second mounting hole groups, each including multiple second fixing holes; the second fixing holes correspond one-to-one with the first fixing holes; the base has two third mounting hole groups, each including multiple third fixing holes; the third fixing holes correspond one-to-one with the second fixing holes; a first fixing bolt passes through the first mounting hole, and the threaded end of the first fixing bolt passes through the second fixing hole and is threadedly connected to the third fixing hole.
[0010] Preferably, the lower limiting plate has a fourth mounting hole at each of its four corners; the base has a fifth mounting hole corresponding to each of the fourth mounting holes; the upper limiting plate has a mounting through hole corresponding to each of the fourth mounting holes; a second fixing bolt passes through the fourth mounting hole, and the threaded end of the second fixing bolt is threaded into the fifth mounting hole; the maximum outer diameter of the second fixing bolt is smaller than the inner diameter of the mounting through hole.
[0011] Preferably, the first fixing bolt and the second fixing bolt are the same bolt.
[0012] The present invention achieves the following technical advantages over the prior art: The limiting and avoidance composite positioning fixture provided by this utility model provides a clear and unified coaxial reference for the assembly of the center conductor and ferrite by coaxially setting the placement through hole of the upper limiting plate and the bottom center hole of the lower limiting plate. Multiple branch elongated holes of the upper limiting plate are distributed circumferentially around the placement center hole and correspond one-to-one with each cantilever end of the center conductor. Similarly, multiple avoidance holes on the inner circumferential sidewall of the bottom center hole of the lower limiting plate also correspond one-to-one with each cantilever end of the center conductor. This corresponding structure achieves precise avoidance of the cantilever ends of the center conductor (avoiding deformation or stress concentration caused by the compression of cantilever ends in traditional fixtures) and, through the circumferential limiting effect of the branch elongated holes and avoidance holes, prevents circumferential rotation of the center conductor during assembly, ensuring the angular stability between the center conductor and the ferrite. Furthermore, the depth of the central hole at the bottom of the lower limit plate is greater than the thickness of the central conductor, which can form a suitable accommodating space for the central conductor. Combined with the upper limit plate's limitation on the upper part of the central conductor, it constrains the radial movement of the central conductor from the vertical direction, further improving the relative positional stability. Finally, the vacuum holes on the base corresponding to the position of the bottom central hole can enhance the positional fixation effect of the ferrite and the central conductor during the assembly process through vacuum adsorption, reducing the risk of displacement during the assembly process. Ultimately, through the structural synergy of the upper limit plate, lower limit plate, and base, a full-dimensional precise constraint on the relative position of the central conductor and the ferrite is formed, effectively controlling the coaxial accuracy of the two and improving the structural stability of the circulator / isolator after assembly. Attached Figure Description
[0013] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0014] Figure 1 A schematic diagram of the overall structure of the limit-avoidance composite positioning fixture provided by this utility model; Figure 2 Exploded view of the limit-avoidance composite positioning fixture provided by this utility model; Figure 3 This is a schematic diagram of the structure before assembly, showing the central conductor and ferrite stacked together. Figure 4 A schematic diagram of the finished product structure after the center conductor and ferrite are assembled; Figure 5 The hole structure shape formed by the bottom center hole and the avoidance hole in the limiting and avoidance composite positioning fixture provided by this utility model; Figure 6 A schematic diagram of the upper limit plate in the limit avoidance composite positioning fixture provided by this utility model; Figure 7 A top view of the limiting and avoidance composite positioning fixture provided by this utility model; Figure 8 A top view of the overall structure of a traditional fixture with an enlarged bottom center hole that has no clearance hole and requires actual operating space to be reserved; Figure 9 For the Figure 7 Image of the completed jig assembly; Figure 10 For the Figure 8 Image of the completed jig assembly; Figure 11 for Figure 9 Finished products and Figure 10 Comparison chart of the isolation characteristics of finished products; Figure 12 for Figure 9 Finished products and Figure 10 Comparison of return loss characteristics of port 1 of finished products; Figure 13 for Figure 9 Finished products and Figure 10 Comparison of return loss characteristics of port 2 of finished products; Figure 14 for Figure 9 Finished products and Figure 10 Comparison chart of insertion loss characteristics of finished products.
[0015] In the picture: 1-Upper limit plate; 101-Center hole; 102-Branch elongated hole; 103-Branch short hole; 104-First fixing hole; 105-First fixing bolt; 106-Mounting through hole; 2-Lower limit plate; 201-Bottom center hole; 202-Allowance hole; 203-Second fixing hole; 204-Fourth mounting hole; 205-Second fixing bolt; 3-Base; 301-Vacuum hole; 302-Third fixing hole; 303-Fifth mounting hole; 4-Center conductor; 401-Cantilever end; 402-Middle circular structure; 5-Ferrite. Detailed Implementation
[0016] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.
[0017] The purpose of this invention is to provide a limit-avoidance composite positioning fixture to solve the problems existing in the prior art, improve the coaxial installation accuracy, and improve the stability of the assembly structure.
[0018] To make the above-mentioned objectives, features and advantages of this utility model more apparent and understandable, the utility model will be further described in detail below with reference to the accompanying drawings and specific embodiments.
[0019] Example 1 This embodiment provides a limit-avoidance composite positioning fixture, mainly but not limited to positioning between the central conductor 4 of the circulator and the ferrite 5, such as... Figures 1-14 As shown, the device includes an upper limit plate 1, a lower limit plate 2, and a base 3, which are fixedly arranged from top to bottom. The upper limit plate 1 has a through hole extending vertically, which includes a central hole 101 and multiple branch elongated holes 102. Each branch elongated hole 102 is circumferentially distributed around the axis of the central hole 101 and corresponds to each cantilever end 401 of the central conductor 4. The lower limit plate 2 has a bottom central hole 201 extending vertically, and in the vertical direction, the depth of the bottom central hole 201 is greater than the thickness of the middle part of the central conductor 4. The bottom central hole 201 is coaxially arranged with the central hole 101. Multiple clearance holes 202 are provided on the inner sidewall of the bottom central hole 201, which correspond to each cantilever end 401 of the central conductor 4. Both the upper limit plate 1 and the lower limit plate 2 are fixedly arranged on the base 3, and a vacuum hole 301 is provided on the base 3 at the position corresponding to the bottom central hole 201.
[0020] The placement through hole of the upper limit plate 1 and the bottom center hole 201 of the lower limit plate 2 are coaxially arranged, providing a clear and unified coaxial reference for the assembly of the center conductor 4 and the ferrite 5. Multiple branch elongated holes 102 of the upper limit plate 1 are circumferentially distributed around the placement center hole 101 and correspond one-to-one with each cantilever end 401 of the center conductor 4. Similarly, multiple clearance holes 202 on the inner circumferential sidewall of the bottom center hole 201 of the lower limit plate 2 also correspond one-to-one with each cantilever end 401 of the center conductor 4. This corresponding structure achieves precise clearance of the cantilever ends 401 of the center conductor 4 (avoiding deformation or stress concentration caused by the compression of the cantilever ends 401 by traditional fixtures), and also prevents circumferential rotation of the center conductor 4 during assembly through the circumferential limiting effect of the branch elongated holes 102 and the clearance holes 202, thus ensuring the proper connection between the center conductor 4 and the ferrite 5. Angular accuracy; furthermore, the depth of the bottom center hole 201 of the lower limit plate 2 is greater than the thickness of the middle part of the center conductor 4, which can form a suitable accommodating space for the middle part of the center conductor 4. Together with the upper limit plate 1 limiting the upper part of the center conductor 4, it constrains the radial movement of the center conductor 4 from the vertical direction, further improving the relative position stability; finally, the vacuum hole 301 set on the base 3 at the position corresponding to the bottom center hole 201 can enhance the position fixation effect of ferrite 5 and center conductor 4 during the assembly process through vacuum adsorption, reducing the risk of displacement during the assembly process. Finally, through the structural synergy of the upper limit plate 1, lower limit plate 2 and base 3, a full-dimensional precise constraint on the relative position of the center conductor 4 and ferrite 5 is formed, effectively controlling the coaxial accuracy of the two and improving the structural stability of the circulator / isolator after assembly.
[0021] Among them, the structure of the lower limit piece 2 using a bottom center hole 201 and various clearance holes 202 is compared to that of... Figure 8 With only a single bottom center hole 201, the clearance hole 202 allows for a smaller difference between the inner diameter of the bottom center hole 201 and the diameter of the central circular structure 402 of the center conductor 4, thus achieving higher coaxiality constraint accuracy for the center conductor 4 and the ferrite 5. Since subsequent bending of the three cantilever ends 401 on the center conductor 4 will form a bent structure at its root, the clearance hole 202 can accommodate this. Compared to a single bottom center hole 201, which requires more space to accommodate the bent structure, the clearance hole 202 provides a more efficient solution. The inner diameter of 01 is larger than that of the bottom center hole 201 in the structure with bottom center hole 201 and clearance hole 202. Because a single bottom center hole 201 only has a bottom center hole 201, it is easy to squeeze the root bend of the cantilever end 401 of the center conductor 4 during assembly, resulting in deformation or stress concentration. In the structure with bottom center hole 201 and clearance hole 202, clearance hole 202 can actively provide a space to accommodate the root bend, reducing the risk of stress concentration deformation or breakage at the bend and ensuring the integrity of the center conductor 4.
[0022] Specifically, due to the matching structure of the clearance hole 202 and the bottom center hole 201, an "embedded slot" is formed; the center conductor 4 and the ferrite 5 can be embedded in it, achieving a precise side fit, which significantly suppresses the micro-movement during the assembly and pressing process of the ferrite 5 and the center conductor 4, so that the amount of movement can reach less than 10μm, thus improving positional stability.
[0023] The following is a description of the structural settings for the upper limit plate 1: Among the optional solutions in this embodiment, the more preferred one is as follows: Figure 1 , Figure 2 and Figure 6 As shown, the placement of the through hole also includes multiple branch short holes 103; each branch short hole 103 is circumferentially distributed around the axis of the placement center hole 101, and the branch short holes 103 and branch long holes 102 are arranged opposite each other on both sides of the placement center hole 101; and the branch short holes 103 and branch long holes 102 are directly opposite each other, the width of the branch long hole 102 matches the maximum width of the cantilever end 401 of the center conductor 4 (that is, the width of the branch long hole 102 can be set according to the maximum width of the cantilever end 401 of the center conductor 4, and can be set according to actual needs, it can be the same or the width of the branch long hole 102 can be slightly larger, so as to ensure the relative position of the cantilever end 401 of the center conductor 4 is constrained), and the width of the branch short hole 103 matches the end width of the cantilever end 401 of the center conductor 4 (similar to the setting of the maximum width of the branch long hole 102 and the cantilever end 401 of the center conductor 4, which will not be elaborated further here).
[0024] Specifically, when the central circular structure 402 of the central conductor 4 is pressed to the bottom central hole 201, the cantilever ends 401 around the central conductor 4 move vertically under the constraint of the corresponding clearance holes 202. Since the width of the clearance holes 202 is the same as the width of the cantilever ends 401 of the central conductor 4, the bending accuracy of the cantilever ends 401 of the central conductor 4 is constrained from the beginning. It is also constrained by the branch long holes 102 and the branch short holes 103, which guide the cantilever ends 401 to return to their positions (a circular insulating film will be attached after each cantilever end 401 is bent). The six-point symmetrical layout forms a self-centering constraint, resists external torque, and eliminates circumferential rotation angle deviation.
[0025] Regarding other related settings: Among the optional solutions in this embodiment, the more preferred one is as follows: Figure 1 , Figure 2 and Figure 7 and Figure 8 As shown, in the vertical direction, the upper limit plate 1 and the lower limit plate 2 have the same external dimensions, and the external dimensions of the base 3 are larger than those of the lower limit plate 2; both the upper limit plate 1 and the lower limit plate 2 can be detachably fixed on the base 3.
[0026] Among the optional solutions in this embodiment, the more preferred one is as follows: Figure 1 , Figure 2 and Figures 6-8 As shown, the upper limit plate 1 has two first mounting hole groups, each including multiple first fixing holes 104; the two first mounting hole groups are respectively arranged opposite to each other on both sides of the through hole; the lower limit plate 2 has two second mounting hole groups, each including multiple second fixing holes 203; the second fixing holes 203 correspond one-to-one with the first fixing holes 104; the base 3 has two third mounting hole groups, each including multiple third fixing holes 302; the third fixing holes 302 correspond one-to-one with the second fixing holes 203; a first fixing bolt 105 passes through the first mounting hole, and the threaded end of the first fixing bolt 105 passes through the second fixing hole 203 and is threadedly connected to the third fixing hole 302.
[0027] Among the optional solutions in this embodiment, the more preferred one is as follows: Figure 1 , Figure 2 and Figures 6-8 As shown, the lower limit plate 2 has a fourth mounting hole 204 at each of its four corners; the base 3 has a fifth mounting hole 303 corresponding to the fourth mounting hole 204; the upper limit plate 1 has a mounting through hole 106 corresponding to the fourth mounting hole 204; a second fixing bolt 205 passes through the fourth mounting hole 204, and the threaded end of the second fixing bolt 205 is threaded into the fifth mounting hole 303; the maximum outer diameter of the second fixing bolt 205 is smaller than the inner diameter of the mounting through hole 106.
[0028] Among the optional solutions in this embodiment, the more preferred one is as follows: Figure 1 and Figure 2 As shown, the first fixing bolt 105 and the second fixing bolt 205 are the same bolt.
[0029] Specifically, avoidance (protecting the cantilever) and constraint (suppressing movement / angle) are traditionally conflicting. This structure achieves both physical avoidance and geometric constraint through a single-slot design, simplifying fixture complexity and making it suitable for mass production.
[0030] The limiting and avoidance composite positioning fixture provided in this embodiment can realize the relative axial movement gap between the center conductor 4 and the ferrite 5 (such as... Figure 10 The thickness of the sample is ≤10μm, which improves the high-frequency isolation of the device; the assembly angle error is ≤0.3°, which ensures the symmetry of the magnetic circuit and optimizes the insertion loss and bandwidth; the cantilever end 401 of the center conductor 4 is free from compression deformation, avoids stress concentration, extends the device life, reduces the risk of breakage of the center conductor 4 (copper sheet), and saves material costs; the assembly consistency is improved, manual adjustment is reduced, the production line yield is improved, and the device stability is guaranteed.
[0031] To demonstrate that the limiting and avoidance composite positioning fixture provided in this embodiment can optimize the assembly of the center conductor 4 and the ferrite 5, this embodiment uses [a specific method / technology] on a 5mm isolator with a center frequency of 1.62GHz. Figure 7 The completed jig assembly (hereinafter referred to as the improved one) and the jig assembly product Figure 8 The assembled fixture (hereinafter referred to as "before improvement") is used to assemble the isolator. The isolation level of the finished product was tested and obtained as follows: Figure 11 As shown, the improved positioning and assembly of the center conductor 4 and ferrite 5 are more precise, the symmetry of the center conductor 4 is better, and the ferrite 5 material achieves a more uniform gyromagnetic state under the action of the bias magnetic field, significantly improving the isolation of the finished device. The return loss at ports 1 and 2 of the finished device was measured as follows: Figure 12 , 13 As shown, the isolator's center frequency is designed to be 1.62 GHz. After improvement, the resonant points of ports 1 and 2 meet the design expectations. However, before improvement, due to the physical asymmetry in the assembly of the center conductor 4 and ferrite 5, impedance mismatch caused by angular deviations or irregular gaps, and the resulting additional reflections, the resonant point of port 1 was higher than the design center frequency, while the resonant point of port 2 was lower than the design center frequency. The insertion loss of the finished product was tested as follows: Figure 14 As shown, the improved assembly of the center conductor 4 and the ferrite 5 reduces the additional losses caused by assembly errors (such as gaps, misalignments, uneven stress, etc.), resulting in lower insertion loss in the improved finished device.
[0032] from Figure 11 , 12 As can be seen from Figures 13 and 14, the characteristics after the improved assembly of the center conductor 4 and ferrite 5 are superior to those before the improvement. By improving the assembly precision and consistency of the center conductor 4 and ferrite 5, the device achieves higher isolation performance (better suppression of interference signals), lower reflection (better port matching), and lower insertion loss (higher signal transmission efficiency). These improvements are crucial for high-performance RF systems that rely on isolators / circulators, leading to higher system efficiency, stronger anti-interference capabilities, and more stable signal quality, thus obtaining isolator / circulator products that meet design performance expectations.
[0033] This utility model uses specific examples to illustrate its principles and implementation methods. The above description of the embodiments is only for the purpose of helping to understand the method and core idea of this utility model. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the idea of this utility model. In summary, the content of this specification should not be construed as a limitation of this utility model.
Claims
1. A composite positioning jig of limit avoidance type, characterized by: This includes an upper limit plate, a lower limit plate, and a base, which are fixedly installed from top to bottom. The upper limit plate has a through hole extending vertically, which includes a central hole and multiple branch holes. Each branch hole is circumferentially distributed around the axis of the central hole and corresponds to each cantilever end of the central conductor. The lower limiting piece has a bottom center hole that extends vertically through the bottom. In the vertical direction, the depth of the bottom center hole is greater than the thickness of the middle part of the center conductor. The bottom center hole is coaxially arranged with the placement center hole. Multiple clearance holes are provided on the inner circumferential sidewall of the bottom center hole. The clearance holes are used to correspond one-to-one with each cantilever end of the center conductor. Both the upper limit plate and the lower limit plate are fixedly mounted on the base, and a vacuum hole is provided on the base corresponding to the position of the bottom center hole.
2. The limiting and avoidance type composite positioning fixture according to claim 1, characterized in that: The placement through hole also includes multiple branch short holes; each of the branch short holes is circumferentially distributed around the axis of the placement center hole, and the branch short holes and the branch long holes are arranged opposite each other on both sides of the placement center hole; the branch short holes and the branch long holes are arranged directly opposite each other, the width of the branch long holes matches the maximum width of the cantilever end of the center conductor, and the width of the branch short holes matches the end width of the cantilever end of the center conductor.
3. The limiting and avoidance type composite positioning fixture according to claim 1, characterized in that: In the vertical direction, the upper limit plate and the lower limit plate have the same external dimensions, and the external dimensions of the base are larger than those of the lower limit plate. Both the upper limit plate and the lower limit plate are detachably fixed on the base.
4. The limiting and avoidance type composite positioning fixture according to claim 3, characterized in that: The upper limit plate has two first mounting hole groups, each of which includes a plurality of first fixing holes; the two first mounting hole groups are respectively arranged opposite to each other on both sides of the through hole. The lower limit piece has two second mounting hole groups, each of which includes multiple second fixing holes; the second fixing holes correspond one-to-one with the first fixing holes. The base is provided with two third mounting hole groups, each of which includes multiple third fixing holes; the third fixing holes correspond one-to-one with the second fixing holes. A first fixing bolt is inserted into the first mounting hole, and the threaded end of the first fixing bolt passes through the second fixing hole and is threadedly connected to the third fixing hole.
5. The limiting and avoidance type composite positioning fixture according to claim 4, characterized in that: The lower limit piece is provided with a fourth mounting hole at each of its four corners; The base is provided with fifth mounting holes that correspond one-to-one with the fourth mounting holes; The upper limit plate is provided with mounting through holes that correspond one-to-one with the fourth mounting hole; A second fixing bolt is inserted into the fourth mounting hole, and the threaded end of the second fixing bolt is threaded into the fifth mounting hole; the maximum outer diameter of the second fixing bolt is smaller than the inner diameter of the mounting through hole.
6. The limiting and avoidance type composite positioning fixture according to claim 5, characterized in that: The first fixing bolt and the second fixing bolt are the same bolt.