Rail cap

Abstract

To provide a rail cap which can properly suppress intrusion of foreign matters into an attachment hole and can be removed from a counterbore with ease.SOLUTION: A rail cap 20 that is fit into a counterbore 16 to block an attachment hole 15 comprises: a lid member 20a formed of a metal material; and a fitting member 20b which is formed of a resin material and is assembled to the lid member 20a. The lid member 20a includes: a plate-shaped circular plate part 21; a short cylinder part 22 protruding from a lower surface of the circular plate part 21; a groove part 23 which is provided at an upper end part of the short cylinder part 22 and in which an external peripheral surface of the short cylinder part 22 is recessed to a radially inner side; and a thinned part 24 which is provided at the circular plate part 21 so as to be positioned on the radially inner side of an internal peripheral surface of the short cylinder part 22. The fitting part 20b includes: an external peripheral surface to make face contact with an internal peripheral surface of the counterbore 16 with the rail cap 20 fitted in the counterbore 16; and a slit 28 extending in a vertical direction of the fitting part 20b.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to an improvement of a rail cap.

Background Art

[0002] Conventionally, a linear guide rail, a slider straddling the guide rail so as to be relatively movable, and a plurality of rolling elements (for example, balls) circulating between rolling grooves formed in the guide rail and the slider are provided. A linear motion guide bearing device is proposed in which the slider is configured to be relatively movable in the axial direction on the guide rail. Such a linear motion guide bearing device is provided with a mounting hole penetrating from the upper surface to the lower surface of the guide rail, a bolt is inserted into the mounting hole, and the screw shaft of the bolt is tightened into a screw hole of a base or the like, whereby it is attached to the base or the like. After such attachment, in order to close the mounting hole, a rail cap made of, for example, metal is fitted into a countersunk hole provided in the upper part of the mounting hole. Thereby, the linear motion guide bearing device suppresses the accumulation of foreign matter in the mounting hole (see Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Summary of the Invention

Problems to be Solved by the Invention

[0004] Incidentally, conventional rail caps have a short cylindrical shape manufactured to a certain thickness. These rail caps have an outer diameter larger than the inner diameter of the counterbore hole, and are fitted into the counterbore hole while the outer circumference is plastically deformed or worn away, and are prevented from coming off by being pressed against the inner circumference of the counterbore hole by elastic force. However, when removing the rail cap from the counterbore hole, the rail cap is destroyed with a tool such as a drill, so the removal work of the rail cap is time-consuming. In addition, the counterbore hole may be damaged by the above work, and there is a risk that the guide rail will not be able to be reused.

[0005] Some conventional rail caps have proposed methods to solve this problem. For example, one method has been proposed in which a part of the top surface is made thin so that a hole can be easily made with a tool such as a screwdriver, and the rail cap can be easily removed from the counterbore hole using that hole (see Patent Document 3). Another proposed method is to bend the top surface upwards to fix the rail cap to the inner circumference of the counterbore hole (see Patent Document 4), or to make the thickness greatest near the center and thin one end so that the other end lifts up when struck with a tool such as a chisel, allowing the rail cap to be easily removed from the counterbore hole (see Patent Document 5). Furthermore, a method has been proposed in which liquid rubber is injected into the space formed between the inner side cover member and the outer side cover member, and the space is filled with liquid rubber and hardened, thereby enabling repeated attachment and removal of the stopper member (see Patent Document 6).

[0006] However, with conventional rail caps, when the slider passes over them, foreign objects caught in the slider can push and deform the top surface of the rail cap, preventing it from maintaining a smooth surface. In such rail caps, foreign objects can accumulate in the gap between the periphery of the top surface of the rail cap and the counterbore hole, potentially causing them to enter the linear motion guide bearing device. Furthermore, the lack of a thin-walled section on the top surface of the rail cap made it difficult to drill holes when removing the rail cap, resulting in time-consuming removal. Thus, conventional rail caps struggled to achieve both ease of removal from the counterbore hole and proper prevention of foreign object intrusion into the counterbore hole (mounting hole).

[0007] This invention was made in view of the above-mentioned problems, and aims to provide a rail cap that properly suppresses the intrusion of foreign matter into the mounting hole and offers excellent workability for removal from the counterbore hole. [Means for solving the problem]

[0008] Therefore, the above objective of the present invention is achieved by the following configurations (1) to (3) relating to the linear motion guide bearing device. (1) A rail cap that is fitted into a counterbore hole provided in the upper part of a mounting hole of a guide rail constituting a linear motion guide bearing device, thereby closing the mounting hole, It comprises a lid member made of a metal material and a ring-shaped fitting member made of a resin material that is assembled to the lid member, The lid member comprises a plate-shaped disc portion and a short cylindrical portion concentric with the disc portion that protrudes from the lower surface of the disc portion. At the upper end of the short cylindrical portion, a groove is formed in which the outer surface of the short cylindrical portion is recessed radially inward. The disc portion is provided with a thin-walled portion that is thinner than the flange portion extending radially outward from the short cylindrical portion, with the lower surface forming a space inside the short cylindrical portion. The fitting member is attached to the groove of the cover member and has an outer surface that makes surface contact with the inner surface of the counterbore hole when the rail cap is fitted into the counterbore hole, and a slit that extends in the vertical direction of the fitting member. Rail cap. (2) The vertical length from the upper end of the cover member to the lower end of the groove is, The length is greater than the vertical length from the upper end of the lid member to the upper end of the outer surface of the fitting member, and less than the vertical length of the rail cap. (1) The linear motion guide bearing device described above. (3) The vertical length from the upper end of the lid member to the upper end of the outer circumferential surface of the fitting member is: The length is greater than the vertical length from the upper end of the cover member to the lower end of the groove, and less than the vertical length of the rail cap. (1) The rail cap described above. [Effects of the Invention]

[0009] According to the rail cap configuration described in (1) above, the intrusion of foreign matter into the mounting hole is properly suppressed by the combination of a cover member and a fitting member. Furthermore, the provision of a thin-walled portion on the disc makes it easier to drill a hole in the thin-walled portion when removing the rail cap from the counterbore hole, thus facilitating the removal process. In addition, because the fitting member that makes surface contact with the counterbore hole is made of resin, the inner surface of the counterbore hole (mounting hole) is less likely to be damaged when removing the rail cap from the counterbore hole, allowing the guide rail to be reused. Thus, the rail cap configuration described above achieves both proper suppression of foreign matter into the mounting hole and excellent workability when removing it from the counterbore hole. Furthermore, the presence of slits in the fitting member makes it easier to attach the fitting member to the lid member.

[0010] According to the rail cap configured as described in (2) above, the contact portion between the fitting member and the counterbore and the contact portion between the fitting member and the lid member (i.e., the groove portion) partially overlap in the vertical direction. As a result, even when the rail cap is inserted into the counterbore and when the rail cap is removed from the counterbore, the fitting member is prevented from coming off the lid member. In other words, the fitting member has excellent holding force to the lid member due to the above configuration.

[0011] According to the rail cap configured as described in (3) above, the contact portion between the fitting member and the counterbore and the contact portion between the fitting member and the lid member (i.e., the groove portion) do not overlap in the vertical direction. As a result, the deformation of the fitting member becomes easy, and the insertion of the rail cap into the counterbore becomes easy. Further, when the deformation of the fitting member becomes easy, when the rail cap is inserted into the counterbore, the outer peripheral portion of the fitting member is not shaved by the counterbore, and thus the decrease in the pressure adhesion force of the rail cap to the counterbore is suppressed.

[0012] The present invention has been briefly described above. Further, the details of the present invention will be further clarified by reading through the embodiments (hereinafter referred to as "embodiments") for carrying out the invention described below with reference to the accompanying drawings.

Brief Description of the Drawings

[0013] [Figure 1] It is a partially broken perspective view for explaining an example of a linear motion guide bearing device including a rail cap according to an embodiment of the present invention. [Figure 2A] It is an exploded perspective view of a rail cap according to a first embodiment of the present invention. [Figure 2B] It is an exploded perspective view showing a modification example of the rail cap shown in FIG. 2A. [Figure 3] It is a schematic cross-sectional view showing a state where the rail cap shown in FIG. 2A is inserted into a counterbore of a guide rail. [Figure 4] It is a first schematic cross-sectional view for explaining a removal process of the rail cap shown in FIG. 2A from the counterbore. [Figure 5]It is a second schematic cross-sectional view for explaining the removal process from the counter bore of the rail cap shown in FIG. 2A. [Figure 6] It is a schematic cross-sectional view showing a state where a rail cap according to a second embodiment of the present invention is fitted into a counter bore of a guide rail. [Figure 7] It is a schematic cross-sectional view showing a state where a rail cap according to a third embodiment of the present invention is fitted into a counter bore of a guide rail. [Figure 8] It is a front view for explaining each dimension of the rail cap shown in FIG. 7. [Figure 9] It is a perspective view of a rail cap according to a fourth embodiment of the present invention.

Mode for Carrying Out the Invention

[0014] Hereinafter, an example of an embodiment of a linear guide bearing device 1 including a rail cap 20 according to the present invention will be described based on the drawings. As the linear guide bearing device 1, a linear guide will be described as an example. Note that the present invention is not limited to the embodiments described below, and can be appropriately modified, improved, etc. In addition, the material, shape, dimensions, number, arrangement location, etc. of each component in the embodiments described below are not limited as long as the present invention can be achieved.

[0015] As shown in FIG. 1, the linear guide bearing device 1 includes a linear guide rail 10 and a slider 30 that is assembled so as to straddle the guide rail 10 and is slidably engaged via a plurality of rolling elements B (balls).

[0016] On the ridge line portion where the upper surface 11 and both side surfaces intersect, a rail-side raceway surface 13 having a substantially 1 / 4 circular arc cross-section is formed in the axial direction, and on both side surfaces, a rail-side raceway surface 14 having a substantially semi-circular cross-section or a Gothic arch shape cross-section is formed in the axial direction.

[0017] Furthermore, the guide rail 10 has multiple mounting holes 15 that penetrate from the top surface 11 to the bottom surface 12, spaced approximately equally in the axial direction. Above each mounting hole 15, a counterbore hole 16 with a larger diameter than the mounting hole 15 is formed, corresponding to each mounting hole 15. Screws 17 for attaching the guide rail 10 to a base or the like are inserted through the mounting holes 15 (see Figure 3).

[0018] The slider 30 comprises a slider body 31, end caps 33 attached to both axial ends of the slider body 31, side seals 34 attached to the axial ends of each end cap 33, and a lubrication nipple 35.

[0019] The slider body 31 is formed in a roughly C-shape with two sleeve portions 32. The inner surfaces of the two sleeve portions 32 have a slider-side track surface 37 that faces the rail-side track surfaces 13 and 14 of the guide rail 10, and also have a rolling element return path 38. The rail-side track surfaces 13 and 14 and the slider-side track surface 37 guide the rolling element B so that it can roll freely and support the load acting on the slider 30 via the rolling element B.

[0020] The end cap 33 is formed in a roughly C-shape and has a curved path 36 that connects the slider-side raceway surface 37 and the rolling element return path 38 of the slider body 31. In other words, the rail-side raceway surfaces 13 and 14, the slider-side raceway surface 37, the rolling element return path 38, and the curved paths 36 at both ends form a rolling element circulation path. Multiple rolling elements B (balls) are loaded to roll freely within the rolling element circulation path. Note that rollers may be used instead of balls as rolling elements B.

[0021] <First Embodiment> Next, a rail cap 20 according to the first embodiment of the present invention will be described. As shown in Figures 1 and 3, the rail cap 20 constitutes a linear motion guide bearing device 1 and is fitted into the counterbore hole 16 of the guide rail 10, thereby closing the mounting hole 15.

[0022] As shown in Figures 2A to 5, the rail cap 20 consists of a lid member 20a made of a metal material such as brass, steel, stainless steel, and aluminum alloy, and a roughly C-shaped ring-shaped fitting member 20b made of a resin material such as synthetic resin that has elastic force.

[0023] In particular, as shown in Figure 2A, the lid member 20a is integrally formed of a substantially circular plate-shaped disc portion 21 and a short cylindrical portion 22 concentric with the disc portion 21 that protrudes downward from the lower surface of the disc portion 21. A groove portion 23 is formed at the upper end of the short cylindrical portion 22 (i.e., the boundary with the disc portion 21), in which the outer circumferential surface of the short cylindrical portion 22 is recessed radially inward. The diameter of the disc portion 21 is set to be slightly smaller than the diameter of the opening of the counterbore hole 16, and the outer diameter of the short cylindrical portion 22 is set to be smaller than the diameter of the counterbore hole 16 and the diameter of the disc portion 21. The short cylindrical portion 22 may also be formed in a tapered shape that decreases in diameter from top to bottom (see Figure 2B).

[0024] The disc portion 21 is provided with a thin-walled portion 24 that is thinner than the flange portion 25, which extends radially outward from the short cylindrical portion 22 and forms a space on its lower surface that is located inside the short cylindrical portion 22 (see Figure 3).

[0025] Similarly, as shown in Figure 2A, the fitting member 20b is formed in a substantially C-shaped ring form with a slit 28 in a part of the circumferential direction. The fitting member 20b is integrally composed of a cylindrical mounting portion 26 that is attached to the groove portion 23 of the lid member 20a and has the same vertical length as the groove portion 23, and a cylindrical fitting portion 27 that is located below the mounting portion 26 and radially outward, and has an outer peripheral surface that makes surface contact with the inner circumferential surface of the counterbore hole 16. The outer diameter of the mounting portion 26 is set to be smaller than the hole diameter of the counterbore hole 16, and the outer diameter of the fitting portion 27 is set to correspond to the hole diameter of the counterbore hole 16. The fitting portion 27 may be formed in a tapered shape that decreases in diameter from top to bottom (see Figure 2B).

[0026] The inner diameter of the fitting portion 27 is larger than the inner diameter of the mounting portion 26, and smaller than the outer diameter of the mounting portion 26. In addition, the mounting portion 26 and the fitting portion 27 are concentric. As a result, the radially outer region of the lower end surface of the mounting portion 26 and the radially inner region of the upper end surface of the fitting portion 27 overlap in the vertical direction.

[0027] The rail cap 20 is completed by attaching the lid member 20a and the fitting member 20b. Specifically, the fitting member 20b is attached from the bottom of the lid member 20a so that the mounting portion 26 of the fitting member 20b fits into the groove portion 23 of the lid member 20a. When attaching the fitting member 20b to the lid member 20a, the fitting member 20b is formed in a roughly C shape, so it is easily elastically deformed to expand in diameter.

[0028] After such mounting, the elastic force of the fitting member 20b causes the outer circumferential surface of the groove 23 and the inner circumferential surface of the mounting portion 26 to come into close contact, and the radially inner region of the lower end surface of the mounting portion 26 is locked into the stepped portion formed by the groove 23 and the short cylindrical portion 22. If the inner diameter of the mounting portion 26 of the fitting member 20b is smaller than the outer diameter of the groove 23 of the cover member 20a, the holding force of the mounting portion 26 to the groove 23 increases. With this, the rail cap 20 is completed.

[0029] To fit the rail cap 20 into the counterbore hole 16 of the guide rail 10, first position the rail cap 20 at the position corresponding to the opening of the counterbore hole 16, then place a backing material (not shown) on the upper surface of the rail cap 20, and in this state, gradually tap the upper surface of the backing material with a hammer or the like. As a result, the fitting portion 27 of the rail cap 20 (i.e., the fitting member 20b) will elastically deform and be fitted into the counterbore hole 16.

[0030] As a result, the disc portion 21, the short cylindrical portion 22, and the mounting portion 26 are positioned with a gap between them and the counterbore hole 16, and the outer surface of the fitting portion 27 and the inner surface of the counterbore hole 16 are in close surface contact, thereby closing the mounting hole 15 (see Figure 3).

[0031] In the first embodiment, as shown in Figure 3, the vertical length L1 from the upper end of the lid member 20a to the lower end of the groove 23 is greater than the vertical length L2 from the upper end of the lid member 20a to the upper end of the fitting portion 27 of the fitting member 20b (specifically, the outer surface of the fitting portion 27 that is in surface contact with the inner surface of the counterbore hole 16), and is smaller than the vertical length L3 of the rail cap 20 (i.e., L2 <L1<L3)。

[0032] In other words, the contact portion between the fitting member 20b (i.e., the fitting portion 27) and the counterbore hole 16, and the contact portion between the fitting member 20b (i.e., the mounting portion 26) and the cover member 20a (i.e., the groove portion 23) overlap by a portion (L1-L2) in the vertical direction. As a result, when fitting the rail cap 20 into the counterbore hole 16 as described above, and when removing the rail cap 20 from the counterbore hole 16 as described later, the fitting member 20b is prevented from coming off the cover member 20a. In other words, the fitting member 20b has excellent holding power to the cover member 20a due to the above configuration.

[0033] Incidentally, when a rail cap is fitted into a counterbore hole, air pressure is generally applied to the fitting area between the rail cap and the counterbore hole, which can cause the rail cap to come out of the counterbore hole. However, in the rail cap 20 according to the embodiment of the present invention, a slit 28 is provided in the fitting member 20b, so that the slit 28 acts as an air discharge passage, preventing the rail cap 20 from coming out of the counterbore hole 16 due to air pressure.

[0034] The process of removing the rail cap 20 from the counterbore hole 16 will now be explained. To remove the rail cap 20 from the counterbore hole 16, place the jig 2 (in this example, a flathead screwdriver) on the upper surface of the thin-walled portion 24, and then, with the jig 2 in this position, tap the upper surface of the jig 2 little by little with a hammer 3 or the like. This will cause the tip of the jig 2 to pierce the thin-walled portion 24 and enter the cylindrical hole of the short cylindrical portion 22 (see Figure 4).

[0035] Then, by tilting the jig 2 and hooking its tip onto the underside of the disc portion 21 (thin-walled portion 24), the rail cap 20 is lifted, and the rail cap 20 is removed from the counterbore hole 16 (see Figure 5). The above describes the process of removing the rail cap 20 from the counterbore hole 16.

[0036] Thus, according to the rail cap 20 of the first embodiment, the intrusion of foreign matter into the mounting hole 15 is properly suppressed by being composed of a cover member 20a and a fitting member 20b. Furthermore, by providing a thin-walled portion 24 on the disc portion 21, when removing the rail cap 20 from the counterbore hole 16, it is easier to drill a hole in the thin-walled portion 24, making the removal work easier. In addition, because the fitting member 20b that makes surface contact with the counterbore hole 16 is made of resin material, when removing the rail cap 20 from the counterbore hole 16, the inner circumferential surface of the counterbore hole 16 (mounting hole 15) is less likely to be damaged, and the guide rail 10 can be reused. In this way, the rail cap 20 of the first embodiment can achieve both proper suppression of the intrusion of foreign matter into the mounting hole 15 and excellent workability when removing it from the counterbore hole 16. Furthermore, the presence of a slit 28 in the fitting member 20b facilitates the attachment of the fitting member 20b to the cover member 20a. The rail cap 20 according to the first embodiment of the present invention has been described above.

[0037] <Second Embodiment> Next, a rail cap 120 according to a second embodiment of the present invention will be described. Similar to the rail cap 20 according to the first embodiment, the rail cap 120 according to the second embodiment constitutes a linear motion guide bearing device 1 and is fitted into the counterbore hole 16 of the guide rail 10, thereby closing the mounting hole 15.

[0038] The only difference between the rail cap 120 according to the second embodiment and the rail cap 20 according to the first embodiment is the relationship between the vertical length from the upper end of the cover member to the lower end of the groove, the vertical length from the upper end of the cover member to the upper end of the fitting portion of the fitting member, and the vertical length of the rail cap. The relationship between the vertical lengths of each part in the second embodiment will be explained below, and explanations other than the differences will be omitted.

[0039] In the second embodiment, as shown in Figure 6, the vertical length L5 from the upper end of the lid member 120a to the upper end of the fitting portion of the fitting member 120b (specifically, the outer surface of the fitting portion that makes surface contact with the inner surface of the counterbore hole 16) is greater than the vertical length L4 from the upper end of the lid member 120a to the lower end of the groove portion 123, and is smaller than the vertical length L6 of the rail cap 120 (L4 <L5<L6)。

[0040] In other words, the contact portion between the fitting member 120b (i.e., the fitting portion) and the counterbore hole 16, and the contact portion between the fitting member 120b (i.e., the mounting portion) and the cover member 120a (i.e., the groove portion 123) do not overlap in the vertical direction. This makes it easier for the fitting member 120b (especially the fitting portion) to undergo elastic deformation, and makes it easier to fit the rail cap 120 into the counterbore hole 16. Furthermore, when the elastic deformation of the fitting member 120b is made easier, when the rail cap 120 is fitted into the counterbore hole 16, the outer circumference of the fitting portion 27 is not scraped by the counterbore hole 16, and consequently, the reduction in the clamping force of the rail cap 120 into the counterbore hole 16 is suppressed.

[0041] The above points highlight the differences from the first embodiment. The rail cap 120, having the same configuration as the rail cap 20 according to the first embodiment, can achieve the same functions and effects. The rail cap 120 according to the second embodiment of the present invention has been described above.

[0042] <Third Embodiment> Next, a rail cap 40 according to the third embodiment of the present invention will be described. Unlike the rail cap 20 according to the first embodiment and the rail cap 120 according to the second embodiment, the rail cap 40 according to the third embodiment is composed of a single component. Specifically, the rail cap 40 is composed of a metal material such as brass, iron, stainless steel, and aluminum alloy.

[0043] Furthermore, as shown in Figure 7, the rail cap 40 comprises a disc portion 41 and a short cylindrical portion 42 that protrudes downward from the peripheral edge of the lower surface of the disc portion 41. The disc portion 41 is provided with a thin-walled portion 43 that forms a space on its lower surface that is inside the short cylindrical portion 42, and is thinner than other parts of the disc portion.

[0044] Here, let D be the outer diameter of the disc portion, T be the vertical length from the upper end of the disc portion to the lower end of the short cylindrical portion, d be the diameter of the thin-walled portion, and t be the vertical length (i.e., plate thickness) of the thin-walled portion (see Figure 8). The rail cap 40 is constructed such that the following relationships exist between its dimensions.

[0045] T ≈ (1 / 4)D d ≈ (1 / 2)D ~ (4 / 5)D t ≈ (1 / 5)T ~ (1 / 3)T

[0046] With the above configuration, the same functions and effects as in the first embodiment can be achieved. In other words, both proper suppression of foreign matter entering the mounting hole 15 and excellent workability for removal from the counterbore hole 16 can be achieved more appropriately. The rail cap according to the third embodiment of the present invention has been described above.

[0047] <Fourth Embodiment> Next, a rail cap 140 according to the fourth embodiment of the present invention will be described. In the rail cap 140 according to the fourth embodiment, the outer surface of the short cylindrical portion 142, which is concentric with the disc portion 141, is knurled (see Figure 9). In other words, the short cylindrical portion 142 has an uneven surface. This makes it easy to deform the rail cap 140 and easy to fit the rail cap 140 into the counterbore hole 16. The other components are configured in the same way as in the third embodiment. The rail cap 140 according to the fourth embodiment of the present invention has been described above. [Explanation of Symbols]

[0048] 1. Linear motion guide bearing device 2. Jig 3. Hammer 10 Guide rails 15 mounting holes 16 Counterbore holes 20,120 Rail caps 20a, 120a Lid member 20b, 120b Fitting members 21,121 Disc section 22,122 Short cylindrical section 23,123 grooves 24,124 Thin-walled section 25 Flange section 26 Mounting part 27 Fitting part 28 slits 30 Slider 40 Rail Caps 41 Disc section 42 Short cylindrical section 43 Thin-walled section B Rolling body

Claims

1. A rail cap that is fitted into a counterbore hole provided in the upper part of a mounting hole of a guide rail constituting a linear motion guide bearing device, thereby closing the mounting hole, It comprises a lid member made of a metal material and a ring-shaped fitting member made of a resin material that is assembled to the lid member, The lid member comprises a plate-shaped disc portion and a short cylindrical portion concentric with the disc portion that protrudes from the lower surface of the disc portion. At the upper end of the short cylindrical portion, a groove is formed in which the outer surface of the short cylindrical portion is recessed radially inward. The disc portion is provided with a thin-walled portion that is thinner than the flange portion extending radially outward from the short cylindrical portion, with the lower surface forming a space inside the short cylindrical portion. The fitting member is attached to the groove of the cover member and has an outer surface that makes surface contact with the inner surface of the counterbore hole when the rail cap is fitted into the counterbore hole, and a slit that extends in the vertical direction of the fitting member. Rail cap.

2. The vertical length from the upper end of the cover member to the lower end of the groove is, The length is greater than the vertical length from the upper end of the lid member to the upper end of the outer circumferential surface of the fitting member, and less than the vertical length of the rail cap. The rail cap according to claim 1.

3. The vertical length from the upper end of the lid member to the upper end of the outer circumferential surface of the fitting member is: The length is greater than the vertical length from the upper end of the cover member to the lower end of the groove, and less than the vertical length of the rail cap. The rail cap according to claim 1.

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