Nut member and hook spanner

Abstract

To provide a nut member which prevents side slip of a hook spanner during tightening / loosening work, and a hook spanner for tightening / loosening the nut member.SOLUTION: A nut member of a collet chuck type tool holder comprises: a thread part arranged in a base end direction; an engagement part arranged in a tip direction; and an inner peripheral part arranged coaxially with the thread part. The engagement part comprises a lock recess and a fitting groove in an outer peripheral surface. The block recess has a substantially rectangular cross-sectional shape in a direction orthogonal to an axial direction of the thread part, the fitting groove has a substantially V-shaped cross-sectional shape in the axial direction of the thread part, and the inner peripheral part penetrates an end face in the base end direction from an end face in the tip direction and comprises a presser face and a rib. The presser face is so formed as to expand a diameter thereof toward the base end direction, and the rib part is located in the base end direction with respect to the presser face and is so formed as to project toward a radial direction inner side.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a nut member used in machine tools used for cutting processes such as lathes, and which tightens a collet chuck that grips the shank of a cutting tool such as a drill or an end mill, and a hook spanner for tightening and loosening this nut member. [Background technology]

[0002] Generally, a rotary tool device is attached to the surface of a tool rest of a machine tool used for turning such as a lathe, and a collet chuck type tool holder is used as an example of a structure for holding a cutting tool. This type of collet chuck type tool holder has a structure in which a collet is inserted into the tip of a holder spindle, a nut member is screwed into a threaded portion formed on the tip of the holder spindle, and the nut member is tightened to reduce the inner diameter of the collet and grip the shank of the cutting tool.

[0003] Conventionally, a hook spanner 100 as shown in Fig. 9 has been used for tightening and loosening such nut members. In the conventional hook spanner 100, an engagement portion 101 formed at the tip of the hook spanner is engaged with an engagement groove formed on the outer peripheral surface of the nut member, and an abutment surface 102 formed at a position away from the engagement portion 101 is brought into abutment with the outer peripheral surface of the nut member to rotate the nut member. With such a conventional hook spanner 100, the abutment surface 102 may shift in the axial direction of the nut member (hereinafter referred to as lateral sliding in this specification) during tightening and loosening of the nut member, and this poses a problem in operational stability.

[0004] Furthermore, as described in Patent Document 1, a hook spanner for tightening such a nut member is known in the related art, which engages with and sets the nut from the side into an engagement groove formed on the outer peripheral surface of the nut to rotate the nut, and is characterized in that when the hook spanner is set on the nut, flange members are provided on both sides of the nut that protrude in a direction perpendicular to the screw-in direction of the nut. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Actual Publication No. 55-66772 Summary of the Invention [Problem to be solved by the invention]

[0006] According to the hook spanner described in Patent Document 1, a flange member provided on the hook spanner can prevent a fastened member such as a collet from falling off when the hook spanner is operated. In addition, the flange member can hold the nut member in the axial direction, which is also effective against the lateral slippage of the hook spanner and is thought to improve workability.

[0007] Known structures for fastening this type of collet chuck with a nut member include a structure in which a female threaded portion provided on the inner surface of the nut member 10' is screwed into a male threaded portion provided on the holder spindle 30' as shown in FIG. 8 (hereinafter referred to as an internal threaded nut structure in this specification), and a structure in which a male threaded portion provided on the outer surface of the nut member 10 is screwed into a female threaded portion provided on the holder spindle 30 as shown in FIG. 1 (hereinafter referred to as an external threaded nut structure in this specification).

[0008] When an externally threaded nut structure as shown in Fig. 1 is adopted as the fastening structure of the collet chuck, it is possible to suppress the protrusion amount L1 of the nut member 10 from the holder spindle 30. This has the advantage that the distance from the tool post surface to the end face of the nut member 10 is shortened, and a wide machining range of the workpiece can be secured. In addition, the distance from the tool post surface to the cutting tool is also shortened, so the rigidity of the entire rotary tool device can be increased.

[0009] However, such an externally threaded nut structure can shorten the amount of protrusion L1 of the nut member 10 from the holder spindle 30, while at the same time reducing the exposed portion of the outer circumferential surface of the nut member 10. As a result, when tightening or loosening the nut member 10, the range in which the hook spanner engages with the outer circumferential surface of the nut member 10 becomes narrow in the axial direction of the nut member 10. This requires the hook spanner to be made thinner, which poses the problem of making the hook spanner more susceptible to lateral slippage during work.

[0010] In addition, the hook spanner described in Patent Document 1 can be applied when fastening a nut member with an internal thread nut structure to prevent lateral slippage, but cannot be applied when fastening a nut member with an external thread nut structure because the flange member interferes with the nut member.

[0011] Therefore, the present invention has been made in consideration of the above-mentioned matters, and an object of the present invention is to provide a nut member that can prevent the hook spanner from slipping sideways during tightening and loosening operations and increase operational stability, even if the fastening structure of a collet chuck type tool holder is an external threaded nut structure in which the exposed portion of the outer circumferential surface of the nut member is small, and a hook spanner for tightening and loosening this nut member. [Means for solving the problem]

[0012] The present invention has been made to achieve the above object and has the following features.

[0013] The nut member according to the present invention is a nut member for a collet chuck type tool holder, and comprises a threaded portion arranged in a base end direction, an engaging portion arranged in a tip end direction, and an inner peripheral portion arranged coaxially with the threaded portion, the engaging portion having an locking recess and a fitting groove on an outer peripheral surface, the locking recess having a cross-sectional shape in a direction perpendicular to the axial direction of the threaded portion that is substantially rectangular, the fitting groove having a cross-sectional shape in the axial direction of the threaded portion that is substantially V-shaped, the inner peripheral portion penetrating from the end face in the tip end direction to the end face in the base end direction and comprising a pressing surface and a rib, the pressing surface being formed so as to expand in diameter toward the base end direction, and the rib being arranged in the base end direction relative to the pressing surface and formed so as to protrude radially inward.

[0014] In the nut member according to the present invention, it is preferable that a plurality of the locking recesses are disposed at equal intervals along the outer circumferential surface of the engagement portion.

[0015] In the nut member according to the present invention, it is preferable that the locking recess communicates with the end face in the distal direction.

[0016] In the nut member according to the present invention, it is preferable that the fitting groove is formed in an annular shape along an outer circumferential surface of the engagement portion.

[0017] In the nut member according to the present invention, it is preferable that the threaded portion has a thread groove formed on an outer circumferential surface thereof.

[0018] The hook spanner of the present invention is a hook spanner for rotating the nut member of the present invention, and comprises a handle portion and a hooking head, the hooking head comprising an arc portion, an engaging claw that engages with the locking recess of the nut member, and a fitting portion that fits into the fitting groove of the nut member, the arc portion extending in an arc shape from one end of the handle portion, the engaging claw extending radially inward from one end of the arc portion, and the fitting portion extending radially inward from the other end of the arc portion.

[0019] In the hook spanner according to the present invention, it is preferable that the fitting portion has a cross-sectional shape in a thickness direction of the arcuate portion formed into a substantially V-shape corresponding to the fitting groove.

[0020] In the hook spanner according to the present invention, it is preferable that the engaging claw has, at a tip end in a direction in which the engaging claw extends, an inclined surface that inclines toward an inner surface of the arc portion.

[0021] The above summary of the invention does not list all of the features necessary for the present invention, and any subcombination of these features may also constitute an invention. Effect of the Invention

[0022] According to the nut member and hook spanner of the present invention, it is possible to prevent the hook spanner from slipping sideways when tightening or loosening the nut member, thereby improving the operational stability. [Brief description of the drawings]

[0023] [Figure 1] FIG. 2 is a cross-sectional view showing an example of a collet chuck to which a nut member according to an embodiment of the present invention is attached. [Diagram 2] FIG. 4 is a front view of the nut member according to the embodiment of the present invention as viewed from the tip end direction. [Diagram 3] Cross section AA of Figure 2. [Figure 4] FIG. 1 is a perspective view showing a hook spanner according to an embodiment of the present invention. [Diagram 5] FIG. 1 is a front view of a nut member according to an embodiment of the present invention, showing a state in which the hook spanner according to the embodiment of the present invention is engaged with the nut member according to the embodiment of the present invention, as viewed from the tip of the nut member; [Figure 6] Cross-sectional view taken along line B-B in FIG. 5 . [Figure 7] Enlarged view of part C in Figure 6. [Figure 8] FIG. 1 is a cross-sectional view showing an example of a collet chuck having an internal threaded nut structure to which a conventional nut member is attached. [Figure 9] FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Preferred embodiments for carrying out the present invention will be described below with reference to the drawings. Note that the following embodiments do not limit the inventions according to the claims, and all of the combinations of features described in the embodiments are not necessarily essential to the solution of the invention.

[0025] Fig. 1 is a cross-sectional view showing an example of a collet chuck to which a nut member according to an embodiment of the present invention is attached, Fig. 2 is a front view of the nut member according to an embodiment of the present invention as viewed from the tip direction, and Fig. 3 is a cross-sectional view taken along line AA in Fig. 2. In this specification, the terms "tip direction" and "base direction" are defined as the directions and orientations indicated by the arrows in Fig. 1 and Fig. 3. The same applies to the arrows in Fig. 8 described later.

[0026] As shown in FIG. 1, a nut member 10 according to the present invention is detachably attached to the tip end of a holder spindle 30 of a rotary tool device used in a machine tool.

[0027] The holder spindle 30 is a substantially cylindrical part, and the collet 40 and the shank of a cutting tool (not shown) are inserted into the inner diameter side. A pressing surface 31 that comes into contact with the collet 40 is formed on the cylindrical inner surface of the tip of the holder spindle 30. The pressing surface 31 is formed as a tapered surface that expands in diameter toward the tip surface of the holder spindle 30.

[0028] The collet 40 is a generally cylindrical part, and has a tapered surface 41 on the outer circumferential surface in the base end direction, a tip abutment surface 42 on the outer circumferential surface in the tip end direction, and an annular groove 43 between the tapered surface 41 and the tip abutment surface 42. The tapered surface 41 abuts against the pressing surface 31 of the holder spindle 30, and is formed as a tapered surface with an angle corresponding to the pressing surface 31. The tip abutment surface 42 abuts against the pressing surface 17 of the nut member 10, which will be described later, and is formed as a tapered surface with an angle corresponding to the pressing surface 17. A tool insertion hole 44 for inserting the shank of a cutting tool (not shown) is formed on the inside of the collet 40. The tool insertion hole 44 is normally in an expanded state, and the shank of the cutting tool can be easily inserted. In addition, the collet 40 has a plurality of slits (not shown) extending in the axial direction. The collet 40 is supported at its front end by the nut member 10 and at its rear end by the holder main shaft 30 .

[0029] 2 and 3, the nut member 10 is a substantially cylindrical part and includes a threaded portion 11 that screws into the holder spindle 30, and an engagement portion 12 that is disposed in the distal direction relative to the threaded portion 11. The nut member 10 also includes an inner periphery 15 that passes through from the end face in the base direction to the end face in the distal direction.

[0030] The threaded portion 11 is, for example, a male screw having a thread groove formed on the outer circumferential surface of the nut member 10, and is screwed into a female screw portion formed at the tip of the holder spindle 30. The thread size of the threaded portion 11 is appropriately determined depending on the size of the collet 40 supported by the nut member 10.

[0031] As shown in Fig. 1, the outer circumferential surface of the engaging portion 12 is exposed when the nut member 10 is attached to the holder spindle 30. As shown in Fig. 3, the engaging portion 12 includes a fitting groove 13 formed in an annular shape along the outer circumferential surface, and a locking recess 14 formed so as to be recessed radially from the outer circumferential surface.

[0032] As shown in FIG. 3, the fitting groove 13 is formed so that the cross section in the axial direction of the nut member 10 is substantially V-shaped. The angle α of the fitting groove 13 is preferably formed symmetrically with respect to a reference plane S that passes through the apex of the substantially V-shape and extends in a direction perpendicular to the axial direction of the nut member 10. The angle α is preferably 60 to 100 degrees, for example, and more preferably 90 degrees. The width W1 of the fitting groove 13 in the central axis direction is formed narrower than the thickness T of the hook spanner 20 described later, and is preferably 1.5 to 3.5 mm, for example, and more preferably 2.0 mm. The shape of the groove bottom of the fitting groove 13 is preferably formed in a small arc shape.

[0033] The locking recess 14 is formed in a substantially rectangular shape when viewed from the tip end direction of the nut member 10, as shown in Fig. 2. The locking recess 14 is also formed in a substantially rectangular shape in a cross section perpendicular to the axial direction of the threaded portion 11. It is preferable that a plurality of the locking recesses 14 are disposed at equal intervals along the outer circumferential surface of the nut member 10. As an example, it is preferable that the locking recesses 14 are formed at 4 to 8 locations along the outer circumferential surface, and more preferably at 6 locations along the outer circumferential surface.

[0034] Further, the locking recess 14 is formed so that the depth D2 in the radial direction of the nut member 10 is deeper than the groove depth D1 of the fitting groove 13. As an example, the depth D2 of the locking recess 14 is preferably 2 to 4 mm. This allows the engagement claw 24 of the hook spanner 20, which will be described later, to be reliably engaged with the locking recess 14.

[0035] The width W2 of the locking recess 14 in the tangential direction of the outer circumferential surface is formed to correspond to the width W3 of the engaging claws 24 of the hook spanner 20 described later, and is preferably 3 to 6 mm, for example. The locking recess 14 may be formed to communicate with the end face of the nut member 10 in the tip direction, as shown in FIG.

[0036] The inner peripheral portion 15 is disposed coaxially with the threaded portion 11, has a through hole 16 that opens from the end face in the distal direction, and penetrates the nut member 10 from the end face in the distal direction to the end face in the proximal direction. A pressing surface 17 that expands in diameter toward the proximal direction is formed on the inner diameter of the inner peripheral portion 15, and at least one rib 18 that protrudes radially inward is formed on the proximal direction relative to the pressing surface 17. The pressing surface 17 abuts against the tip abutting surface 42 of the collet 40, and is formed as a tapered surface that expands in diameter toward the proximal direction so as to correspond to the shape of the tip abutting surface 42. The rib 18 engages with an annular groove 43 of the collet 40.

[0037] Next, the hook spanner 20 used when fastening the nut member 10 according to this embodiment to the holder spindle 30 will be described.

[0038] FIG. 4 is a perspective view showing a hook spanner according to an embodiment of the present invention.

[0039] As shown in FIG. 4, the hook spanner 20 includes a handle portion 21 and a hook head portion 22.

[0040] Handle 21 is a portion for a user to grip, and is formed in a long, narrow plate shape having a uniform thickness T. One end of handle 21 is continuous with hook head 22, and the other end of handle 21 has a through hole formed therein that allows hook spanner 20 to be hung on a wall. Handle 21 may be formed so that its width in a direction intersecting the thickness direction narrows toward one end, while ensuring the strength required for the operation of tightening or loosening nut member 10.

[0041] The hook head 22 comprises an arc portion 23 formed to extend in an arc shape from one end of the handle portion 21, an engagement claw 24 formed on the end of the arc portion 23 away from the handle portion 21 (hereinafter referred to as one end of the arc portion 23), and an engagement portion 25 formed on the end of the arc portion 23 closer to the handle portion 21 (hereinafter referred to as the other end of the arc portion 23).

[0042] 4, the arc portion 23 is formed in an arc shape, is continuous with the handle portion 21, and is formed to have a uniform thickness T. The radius of the inner surface of the arc shape of the arc portion 23 is formed slightly larger than the radius of the outer peripheral surface of the nut member 10 so as to correspond to the radius of the outer peripheral surface of the nut member 10. In addition, the arc portion 23 may be formed so that the radial width of the arc shape narrows toward one end, while ensuring the strength required for the operation of tightening and loosening the nut member 10.

[0043] The engagement claw 24 is formed so as to extend from one end of the arc portion 23 toward the inside in the radial direction of the arc portion 23, and is formed to have a uniform thickness T continuous with the arc portion 23. The extension amount H1 of the engagement claw 24 is formed so as to correspond to the depth D2 of the locking recess 14 of the nut member 10, and is preferably 2 to 5 mm. However, it is important that the engagement claw 24 is formed so that the tip end of the engagement claw 24 in the extension direction does not come into contact with the bottom surface of the locking recess 14 when the engagement claw 24 is engaged with the locking recess 14 of the nut member 10 as described later. In addition, the width W3 of the engagement claw 24 is formed so as to correspond to the width W2 of the locking recess 14 of the nut member 10, and is preferably 2 to 5 mm. In addition, an inclined surface 26 inclined toward the inner surface of the arc portion 23 may be formed at the tip end of the engagement claw 24 in the extension direction.

[0044] The fitting portion 25 is formed so as to extend from the other end of the arc portion 23 radially inward in an arc shape, and is formed to have a uniform thickness T continuous with the arc portion 23. The fitting portion 25 is formed at a circumferential position of the arc portion 23 such that, when the engagement claw 24 is engaged with any one of the locking recesses 14 of the nut member 10, the fitting portion 25 does not overlap with the other locking recesses 14. The extension amount H2 of the fitting portion 25 is formed so as to correspond to the groove depth D1 of the fitting groove 13 of the nut member 10.

[0045] As shown in FIG. 7, the fitting portion 25 has a V-shaped slope 27 formed in a substantially V-shape such that the cross-sectional shape of the arc portion 23 in the thickness direction corresponds to the fitting groove 13 of the nut member 10. The V-shaped slope 27 is preferably formed symmetrically with respect to a reference plane passing through the center of the hook spanner 20 in the thickness direction, and is preferably formed at an angle equal to the angle α of the fitting groove 13 of the nut member 10. However, it is important that the fitting portion 25 is formed so that when the fitting portion 25 is fitted into the fitting groove 13 of the nut member 10 as described later, the V-shaped slope 27 reliably abuts on the slope of the fitting groove 13 and the tip end of the fitting portion 25 in the extending direction does not come into contact with the groove bottom of the fitting groove 13 formed in a small arc shape.

[0046] In the above, the handle portion 21, the arc portion 23, the engaging claws 24, and the fitting portion 25 of the hook spanner 20 have been described as having a uniform thickness T, but the thickness of each portion is not limited to this, and the thickness of each portion may be varied while ensuring the strength required for the tightening and loosening operation of the nut member 10. Furthermore, the thickness T of the arc portion 23, the engaging claws 24, and the fitting portion 25 is set in accordance with the protrusion amount L1 of the nut member 10, and may be set to be thinner than the thickness T' of the conventional hook spanner 100.

[0047] Next, a method for performing the tightening and loosening operation of the nut member 10 according to this embodiment using the hook spanner 20 according to this embodiment will be described.

[0048] FIG. 5 is a front view seen from the tip of the nut member showing a state in which a hook spanner according to an embodiment of the present invention is engaged with a nut member according to an embodiment of the present invention, FIG. 6 is a cross-sectional view taken along line B--B of FIG. 5, and FIG. 7 is an enlarged view of part C of FIG. 6.

[0049] First, as shown in Figures 5 and 6, the engaging claw 24 of the hook spanner 20 is engaged with the locking recess 14 of the nut member 10. At this time, since the engaging claw 24 has an inclined surface 26 formed at its tip, the engaging claw 24 can be smoothly engaged with the locking recess 14. Furthermore, since the locking recess 14 is formed to communicate with the end face of the nut member 10 in the tip direction, the engaging claw 24 can be engaged with the locking recess 14 not only from the outer circumferential surface of the nut member 10, which has a small exposed portion, but also from the end face of the nut member 10 in the tip direction, resulting in excellent operability.

[0050] Next, the fitting portion 25 of the hook spanner 20 is fitted into the fitting groove 13 of the nut member 10. At this time, since the fitting portion 25 is set in advance so as to be positioned so as not to overlap with the locking recess 14, the V-shaped slope 27 of the fitting portion 25 can be reliably brought into contact with the slope of the fitting groove 13.

[0051] After the hook head 22 of the hook spanner 20 is engaged with the engaging portion 12 of the nut member 10 in this manner, the handle portion 21 of the hook spanner 20 is rotated clockwise as viewed in Fig. 5 to tighten the nut member 10. Furthermore, the hook spanner 20 is turned upside down as viewed in Fig. 5, engaged with the nut member 10, and rotated counterclockwise to loosen the nut member. Note that the above explanation has been given for the case where the threaded portion 11 is a right-handed thread. If the threaded portion 11 is a left-handed thread, the rotation directions for the tightening and loosening operations are opposite to those explained above.

[0052] As described above, by bringing the V-shaped inclined surface 27 of the hook spanner 20 into contact with the generally V-shaped inclined surface of the fitting groove 13, the hook spanner 20 and the nut member 10 are firmly engaged in the axial direction of the nut member 10 when tightening or loosening the nut member 10. Therefore, even if the amount of protrusion L1 of the nut member 10 from the holder spindle 30 is small or the thickness T of the hook spanner 20 is thin, it is possible to prevent the hook spanner 20 from sliding sideways or falling off.

[0053] In the above, the case where the hook spanner 20 according to this embodiment is used to tighten and loosen the nut member 10 has been described, but the nut member 10 according to this embodiment can also be tightened and loosened by a conventional hook spanner 100. In this case, the abutment surface 102 of the conventional hook spanner 100 does not fit into the fitting groove 13 of the nut member 10, but since the width W1 of the fitting groove 13 is formed narrower than the thickness T' of the hook spanner 100, the abutment surface 102 of the hook spanner 100 can be brought into contact with the outer peripheral surface of the engagement portion 12 of the nut member 10 to tighten or loosen the nut member 10.

[0054] In the above, the nut member 10 according to the present embodiment is described as being used in a collet chuck having an external thread nut structure in which the threaded portion 11 is a male thread having a thread groove formed on the outer peripheral surface of the nut member 10 and is screwed into a female threaded portion formed at the tip of the holder spindle 30. However, the threaded portion 11 formed on the nut member 10 is not limited to this, and may be used in a collet chuck having an internal thread nut structure in which the threaded portion 11 is a female thread having a thread groove formed on the inner peripheral surface of the nut member 10 and is screwed into a male threaded portion formed at the tip of the holder spindle 30. In addition, the nut member 10 according to the present embodiment is described as being used in a holder for a rotating tool, but may be used in a holder for a fixed tool. It is clear from the claims that such modified or improved forms are also included in the technical scope of the present invention.

[0055] 10 nut member, 11 threaded portion, 12 engaging portion, 13 fitting groove, 14 locking recess, 15 inner circumference, 16 through hole, 17 pressing surface, 18 rib, 20 hook spanner, 21 handle portion, 22 hook head, 23 arc portion, 24 engaging claw, 25 fitting portion, 26 inclined surface, 27 V-shaped inclined surface, 30 holder spindle, 31 pressing surface, 40 collet, 41 tapered surface, 42 tip abutment surface, 43 annular groove, 44 tool insertion hole.

Claims

1. A nut member for a collet chuck type tool holder, The needle includes a threaded portion disposed in a proximal direction, an engagement portion disposed in a distal direction, and an inner peripheral portion disposed coaxially with the threaded portion, The engaging portion has an engaging recess and a fitting groove on an outer circumferential surface, The locking recess has a cross-sectional shape perpendicular to the axial direction of the threaded portion that is generally rectangular, The fitting groove has an axial cross-sectional shape of the threaded portion that is substantially V-shaped, The inner circumferential portion extends from an end face in the distal direction to an end face in the proximal direction, and includes a pressing surface and a rib. The pressing surface is formed so as to expand in diameter toward the base end direction, The rib is disposed in the base end direction relative to the pressing surface and is formed so as to protrude radially inward.

2. The nut member according to claim 1, The nut member is characterized in that a plurality of the locking recesses are arranged at equal intervals along the outer circumferential surface of the engagement portion.

3. The nut member according to claim 1, The nut member is characterized in that the locking recess communicates with the end face in the distal direction.

4. The nut member according to claim 1, The nut member is characterized in that the fitting groove is formed in an annular shape along an outer circumferential surface of the engagement portion.

5. The nut member according to claim 1, The nut member is characterized in that the threaded portion has a thread groove formed on an outer peripheral surface.

6. A hook spanner for rotating the nut member according to any one of claims 1 to 5, The tool has a handle and a hook head. The hook head includes an arc portion, an engagement claw that engages with the locking recess of the nut member, and a fitting portion that fits into the fitting groove of the nut member, The arc portion extends in an arc shape from one end of the handle portion, The engaging claw extends from one end of the arc portion toward a radially inner side of the arc portion, The hook spanner according to claim 1, wherein the fitting portion extends radially inward from the other end of the arc portion.

7. 7. The hook spanner of claim 6, The hook spanner according to claim 1, wherein the arcuate portion has a cross-sectional shape in a thickness direction thereof that is substantially V-shaped corresponding to the fitting groove.

8. 7. The hook spanner of claim 6, The hook spanner according to claim 1, wherein the engaging claw has an inclined surface at a tip end in a direction in which the engaging claw extends, the inclined surface inclining toward an inner surface of the arc portion.

Images