JP7728567B2 - Fastening Tools - Google Patents

Description

The present invention relates to a tightening tool.

Conventionally, as shown in Patent Document 1, some sockets that make up tightening tools are designed to be lightweight by bending part of the outer periphery radially inward.

Specifically, this socket has a fitting hole that fits into the object to be fastened and is hexagonal when viewed from the axial direction, with the outer circumferential surface curved radially inward at locations corresponding to each of the six sides of the fitting hole.

On the other hand, conventional technical knowledge holds that the areas corresponding to the vertices of the mating holes are areas that are subject to significant stress during tightening, and so they are made thicker to ensure mechanical strength. The socket described in Patent Document 1 is proof of this, with the areas on the socket's outer surface that correspond to each of the six vertices of the mating holes forming arcs that bulge outward.

Furthermore, when focusing on the drive angle facing away from the mating hole, conventional technical knowledge suggests that large stress is applied to the area on the outer surface of the socket that corresponds to the corner of the drive angle.

The present invention was developed by challenging this common technical knowledge, questioning the need to add thickness to the area corresponding to the apex of the fitting hole, and carefully examining the areas where mechanical strength is truly required.

Utility Model Registration No. 3135906

And as a result of the above-mentioned thorough investigation, the inventors discovered that the areas that truly require mechanical strength are different from the areas corresponding to the fitting hole and the apex of the insertion angle.

The primary objective of the present invention is to provide a tightening tool that is even lighter than conventional tools while still maintaining mechanical strength.

In other words, the tightening tool according to the present invention is a tightening tool having a tubular portion with a fitting hole formed therein that fits into an object to be tightened, wherein the fitting hole has a polygonal shape when viewed axially, and the side corresponding points on the outer peripheral surface of the tip tubular portion that correspond to the centers of the sides of the fitting hole and the point corresponding points on the outer peripheral surface that correspond to the vertices of the fitting hole are located radially inward of the circumscribing circle of the outer peripheral surface.

The tightening tool according to the present invention is characterized in that it has a cylindrical portion formed with an insertion angle into which the square drive of a handle held by an operator is inserted, and that the side corresponding portions on the outer peripheral surface of the cylindrical portion that correspond to the centers of the sides of the insertion angle and the point corresponding portions on the outer peripheral surface that correspond to the vertices of the insertion angle are located radially inward of the circumscribed circle of the outer peripheral surface.

With the tightening tool configured in this way, the side-corresponding portions and the point-corresponding portions on the outer peripheral surface of the tubular portion are located radially inward of the circumscribing circle of the outer peripheral surface, so that when viewed from the axial direction, there exists a point between the side-corresponding portions and the point-corresponding portions where the circumscribing circle passes, i.e., the point farthest from the center. And, as detailed analysis data will be described later, it is precisely the vicinity of this point that truly requires mechanical strength on the outer peripheral surface of the tubular portion.
Therefore, with the above-described configuration, the mechanical strength of the tubular portion of the socket or the like is ensured while not only the side-corresponding portions but also the point-corresponding portions are positioned radially inward of the circumscribed circle, thereby making it possible to further reduce the weight of the tubular portion compared to conventional methods.

To ensure sufficient mechanical strength, it is preferable that the radial thickness dimension at the point on the outer peripheral surface through which the circumscribed circle passes be greater than the radial thickness dimension at the edge-corresponding location and the radial thickness dimension at the point-corresponding location.

A specific embodiment is one in which at least one of the side-corresponding portions and the point-corresponding portions is provided in a curved region that curves toward the central axis on the outer circumferential surface.
In this case, by providing the side-corresponding portions and point-corresponding portions in the curved region, it is possible to make the object lighter.

In another embodiment, at least one of the side-corresponding portions and the point-corresponding portions is provided in a flat area on the outer peripheral surface that is parallel to the central axis.
This reduces the manufacturing load compared to when side-corresponding portions and point-corresponding portions are provided in curved regions.

Incidentally, if the socket has a regular shape along the circumferential direction, the stress applied to the socket during work is dispersed to multiple locations.
In this case, if a large enough stress is applied to the socket to cause it to break, it may be impossible to predict which point the break will occur, and if it breaks in multiple places, there is a concern that fragments may fly around.

Therefore, in order to break the ring safely, it is preferable that one location in the circumferential direction is formed as a stress concentration location where stress is concentrated more than other locations.
With this configuration, even if a large stress is applied, the breakage occurs at the stress concentration point, making it possible to prevent fragments from scattering and to break the structure safely.

In order to form a stress concentration point without making the socket have a complex shape, it is preferable that the stress concentration point be formed between one of the vertices of the fitting hole and the corresponding point.

This invention, configured in this way, can provide a tightening tool that is lighter than conventional tools while ensuring the mechanical strength of the tubular portion of the socket, etc.

FIG. 1 is a schematic diagram showing a tightening tool according to an embodiment. Analysis data of the stress applied to the tip tube part of the socket. FIG. 1 is a perspective view schematically illustrating a socket according to an embodiment of the present invention. FIG. 4 is a plan view schematically showing the tip tube portion of the embodiment as viewed from the axial direction. Analysis data for the stress applied to the base end cylindrical part of the socket. FIG. 4 is a plan view schematically showing the base end tube portion of the embodiment as viewed from the axial direction. FIG. 10 is a perspective view schematically showing a socket according to another embodiment. FIG. 10 is a cross-sectional view schematically showing the inside of a socket according to another embodiment. FIG. 10 is a perspective view schematically showing a socket according to another embodiment. FIG. 10 is a perspective view schematically showing a socket according to another embodiment. FIG. 10 is a cross-sectional view schematically showing the inside of a socket according to another embodiment. FIG. 10 is a plan view schematically showing a tip tube portion of another embodiment as viewed from the axial direction. FIG. 10 is a plan view schematically showing a tip tube portion of another embodiment as viewed from the axial direction. FIG. 10 is a plan view schematically showing a tip tube portion of another embodiment as viewed from the axial direction. FIG. 10 is a plan view schematically showing a tip tube portion of another embodiment as viewed from the axial direction.

The tightening tool according to the present invention will be described below with reference to the drawings.

1, a tightening tool 200 according to the present invention is a socket wrench used for tightening an object Z such as a bolt or nut, and includes a handle X that is held by a worker and a socket 100 attached to the handle X. The tightening tool 200 may be a manual tool (hand tool), or may be a power tool such as an electric tool, an air tool, or a hydraulic tool.
This fastening tool 200 is characterized by the socket 100, which will be described in detail below.

As shown in Figure 1, the socket 100 is cylindrical and has a fitting hole h1 into which the object to be fastened Z fits, and an insertion angle h2 facing away from the fitting hole h1 and into which the square drive X1 provided on the head of the handle X is inserted. It has a tip tube portion 10 in which the fitting hole h1 is formed, and a base end tube portion 20 in which the insertion angle h2 is formed.

The distal tube portion 10 and the proximal tube portion 20 are arranged coaxially. There are no particular limitations on the external dimensions of the distal tube portion 10 or the proximal tube portion 20; the external dimensions of the distal tube portion 10 may be smaller than or larger than the external dimensions of the proximal tube portion 20, or they may be the same. Note that the external dimensions referred to here refer to the diameter of the circumscribed circle when viewed axially.

The fitting hole h1 is fitted into the fastening object Z, and its planar shape when viewed from the axial direction is polygonal. Note that a polygonal shape here refers to a shape with multiple vertices and multiple sides connecting adjacent vertices, and examples include a square, a hexagon, a dodecagon formed by two hexagons stacked with a 30-degree offset (double hexagon), and a dodecagon formed by three squares stacked with a 30-degree offset (triple square).

In this embodiment, the fitting hole h1 has a hexagonal planar shape, but just as the tightening object Z has a variety of shapes, the fitting hole h1 may have a variety of planar shapes.

The socket angle h2 is the angle into which the square drive X1 of the handle X is inserted, and its planar shape when viewed from the axial direction is polygonal.

In this embodiment, the insertion angle h2 has a rectangular planar shape. Note that the size of the insertion angle h2 can be changed as needed, just as there are various sizes of square drives X1.

In this embodiment, as shown in Figure 1, the fitting hole h1 and the insertion angle h2 are connected, and the base end tubular portion 20 is provided with a communication hole h3 that is located between the fitting hole h1 and the insertion angle h2 and connects them.

This communicating hole h3 is smaller in size than the fitting hole h1 and the insertion angle h2 when viewed from the axial direction, and in this embodiment, its planar shape is circular. However, the shape of the communicating hole h3 may be modified as appropriate.

The data shown in Figure 2 is analysis data of the stress applied to a socket with a circular outer surface in plan view when the socket is used to tighten an object. It also shows that greater stress is applied to the white areas of the outer surface of the tip tube than to the black areas.

As can be seen from this analysis data, greater stress is applied to point B on the outer surface of the tip tube portion than to point A, which corresponds to the apex of the fitting hole. In other words, point B on the outer surface of the tip tube portion needs to have greater mechanical strength than point A, which corresponds to the apex of the fitting hole. Note that in Figure 2, adjacent point B is adjacent to the left of point A, which corresponds to the apex, but when loosening the tightened object, adjacent point B appears adjacent to the right of point A, which corresponds to the apex.

In order to achieve a lightweight socket 100 while maintaining the mechanical strength of the tip tube portion 10, the socket 100 of this embodiment is configured so that, as shown in Figures 3 and 4, the edge corresponding portion 12 on the outer peripheral surface of the tip tube portion 10 that corresponds to the center M1 of the side portion 11 of the fitting hole h1 and the point corresponding portion 14 on the outer peripheral surface that corresponds to the vertex 13 of the fitting hole h1 are located radially inward of the circumscribed circle C1 of the outer peripheral surface. Note that in Figure 4, for ease of understanding, the outline of the outer peripheral surface of the tip tube portion 10 is drawn with a thicker line than the outlines of other portions.

More specifically, the fitting hole h1 is formed by the inner circumferential surface of the tip tube portion 10, and each of the sides 11 of the fitting hole h1 is a straight line from one vertex 13 on the inner circumferential surface to the adjacent vertex 13 when viewed axially. The vertices 13 here are configured to come into surface contact with the object Z to be fastened, and specifically have a rounded groove shape (R-shape) that bulges outward in the radial direction without being angular.

The side corresponding point 12 is the intersection point between the first imaginary line L1, which passes from the center O1 of the fitting hole h1 through the center M1 of the side portion 11, and the outer peripheral surface of the tip tube portion 10.

On the other hand, the point-corresponding location 14 is the intersection of a second imaginary line L2, which runs from the center O1 of the fitting hole h1 through the vertex 13 on the inner surface of the tip tube portion 10, and the outer surface of the tip tube portion 10.

With the above-described configuration, a passing point P1 through which the circumscribed circle C1 passes exists between the side corresponding point 12 and the point corresponding point 14 on the outer peripheral surface of the distal end tube portion 10.

In this configuration, the radial thickness dimension at the passing point P1 is greater than the radial thickness dimension at the side corresponding point 12 and the radial thickness dimension at the point corresponding point 14. In other words, the passing point P1 is thicker than the side corresponding point 12 and the point corresponding point 14.

However, in light of the analysis data shown in Figure 2, this passing point P1 is the point where greater stress is applied during tightening than the edge corresponding point 12 or the point corresponding point 14.

In this embodiment, the side-corresponding portions 12 and point-corresponding portions 14 are provided in curved regions S1 and S2 on the outer circumferential surface of the distal tube portion 10, which curve toward the central axis.

More specifically, the side-corresponding portion 12 is provided in the first curved region S1, which is formed over a predetermined angle range from the side-corresponding portion 12.

On the other hand, the point corresponding portion 14 is provided in the second curved region S2, which here is formed over a predetermined angular range from the point corresponding portion 14.

The first curved region S1 and the second curved region S2 are formed alternately in the circumferential direction, and the above-mentioned passing point P1 is provided between adjacent first curved region S1 and second curved region S2.

In this embodiment, the first curved region S1 and the second curved region S2, which are adjacent to each other, are formed so as to intersect, and the intersection point is the passing point P1 described above.

The data shown in Figure 5 is analysis data obtained by analyzing the stress applied to a socket with a circular outer circumferential surface at the base end when the socket is used to tighten an object. It also shows that greater stress is applied to the white areas than the black areas on the inner circumferential surface of the drive. At first glance, the analysis data in Figure 5 appears to show that the size of the square drive is larger than the drive angle. However, this is because the shape shown in the lower part of Figure 5 was used as a test specimen to simulate a square drive.

As can be seen from this analysis data, greater stress is applied to point D on the outer surface of the tubular base end portion than to point C, which corresponds to the apex of the drive angle. In other words, point D on the outer surface of the tubular base end portion needs to have greater mechanical strength than point C, which corresponds to the apex of the drive angle. Note that in Figure 5, adjacent point D is adjacent to the right side of point C, which corresponds to the apex, but if the socket were tightened in the opposite direction, adjacent point D would appear adjacent to the right side of point C, which corresponds to the apex.

In order to achieve a lightweight socket 100 while maintaining the mechanical strength of the tubular base end portion 20, the socket 100 of this embodiment is configured so that, as shown in Figures 3 and 6, the side corresponding portion 22 on the outer peripheral surface of the tubular base end portion 20 that corresponds to the center M2 of the side portion 21 of the drive angle h2 and the point corresponding portion 24 on the outer peripheral surface that corresponds to the vertex 23 of the drive angle h2 are located radially inward of the circumscribed circle C2 of the outer peripheral surface. Note that in Figure 6, for ease of understanding, the outline of the outer peripheral surface of the tubular base end portion 20 is drawn with a thicker line than the outlines of other portions.

More specifically, the insertion angle h2 is formed by the inner circumferential surface of the base end tubular portion 20, and each side 21 of the insertion angle h2 is a straight line segment from one vertex 23 on the inner circumferential surface to the adjacent vertex 23 when viewed axially. The vertices 23 here are configured to be in surface contact with the square drive X1, and specifically, they are not angular but have a rounded groove shape (R-shape) that bulges outward in the radial direction.

The side corresponding point 22 is the intersection point between a third imaginary line L3, which passes from the center O2 of the insertion angle h2 through the center M2 of the side portion 21, and the outer peripheral surface of the base end tubular portion 20.

On the other hand, the point-corresponding location 24 is the intersection of a fourth imaginary line L4, which passes from the center O2 of the insertion angle h2 through the vertex 23 on the inner surface of the base end tubular portion 20, and the outer surface of the base end tubular portion 20.

With the above-described configuration, a passing point P2 through which the circumscribed circle C2 passes exists between the side corresponding point 22 and the point corresponding point 24 on the outer peripheral surface of the base end tubular portion 20.

In this configuration, the radial thickness dimension at the passing point P2 is greater than the radial thickness dimension at the side corresponding point 22 and the radial thickness dimension at the point corresponding point 24. In other words, the passing point P2 is thicker than the side corresponding point 22 and the point corresponding point 24.

However, in light of the analysis data shown in Figure 5, this passing point P2 is the point where greater stress is applied during the tightening operation than the edge-corresponding point 22 or the point-corresponding point 24.

In this embodiment, the side-corresponding portions 22 and point-corresponding portions 24 are provided in curved regions T1 and T2 on the outer peripheral surface of the base end tubular portion 20, which curve toward the central axis.

More specifically, the side-corresponding portion 22 is provided in the first curved region T1, which is formed over a predetermined angle range from the side-corresponding portion 22.

On the other hand, the point corresponding portion 24 is provided in the second curved region T2, which here is formed over a predetermined angular range from the point corresponding portion 24.

The first curved regions T1 and second curved regions T2 are formed alternately in the circumferential direction, and the above-mentioned passing point P2 is provided between adjacent first curved regions T1 and second curved regions T2.

In this embodiment, a bulging region T3 that bulges outward is provided between the adjacent first curved region T1 and second curved region T2, and a passing point P2 is provided in this bulging region T3.

With the tightening tool 200 configured in this manner, the side-corresponding portion 12 and point-corresponding portion 14 of the socket 100 are located radially inward of the circumscribing circle of the tip tube portion 10, so the thickness dimension of the passing portion P1, which requires mechanical strength, can be made larger than the thickness dimensions of the passing portion P1 and the point-corresponding portion 14. This allows for a reduction in weight while ensuring the mechanical strength of the tip tube portion 10.

Furthermore, because the side corresponding portion 22 and the point corresponding portion 24 are located radially inward of the circumscribing circle of the base end tubular portion 20, the thickness dimension of the passing portion P2, which requires mechanical strength, can be made larger than the thickness dimensions of the passing portion P2 and the point corresponding portion 24. This allows for a reduction in weight while ensuring the mechanical strength of the base end tubular portion 20.

Furthermore, because the side corresponding portions 12, tip point corresponding portions, side corresponding portions 22, and point corresponding portions 24 are provided in the curved regions S1, S2, T1, and T2, respectively, the socket 100 can be made lighter.

In addition, a lightening hole 30 is provided on the inner surface of the base end tubular portion 20, further reducing the weight.

Note that the present invention is not limited to the above-described embodiment.

For example, as shown in FIG. 7, the socket 100 according to the present invention may have an intermediate tubular portion 40 interposed between the distal tubular portion 10 and the proximal tubular portion 20, and having, for example, a circular planar outer circumferential surface.
In this case, in the above embodiment, the communication hole h3 connecting the fitting hole h1 and the insertion angle h2 is provided in the base end cylindrical portion, but as shown in Figure 8, the communication hole h3 may be provided in the intermediate cylindrical portion 40.
9, the intermediate tubular portion 40 may be longer in the axial direction than the distal tubular portion 10 and the proximal tubular portion 20. Although not shown, the intermediate tubular portion 40 may have a recessed outer circumferential surface that is curved radially inward, for example.

Furthermore, the communication hole h3 is not necessarily required; for example, as shown in Figures 10 and 11, the fitting hole h1 and the insertion angle h2 may be directly connected.

In addition, in the above embodiment, the side corresponding portions 12 and point corresponding portions 14 of the tip tube end are provided in the curved regions S1 and S2, but as shown in Figure 12, some or all of the side corresponding portions 12 and point corresponding portions 14 may be provided in flat regions F1 and F2 parallel to the central axis on the outer peripheral surface of the tip tube portion.
The same applies to the side corresponding portions 22 and point corresponding portions 24 of the base end tubular portion, and some or all of them may be provided in a flat area parallel to the central axis on the outer circumferential surface of the tip end tubular portion.

Furthermore, in the above embodiment, all of the side corresponding locations 12 and point corresponding locations 14 were located radially inward of the circumscribing circle C1, but only some of the side corresponding locations 12 and point corresponding locations 14 may be located radially inward of the circumscribing circle C1, for example, by locating every other side corresponding location 12 or point corresponding location 14 in the circumscribing circle C1 in the circumscribing direction. The same can be said for the positional relationship between the side corresponding locations 22 and point corresponding locations 24 and the circumscribing circle C2.

In addition, in the above embodiment, the vertices 13, 24 of the fitting hole h1 and the socket angle h2 are rounded and configured to make surface contact with the fastening object Z, but the vertices 13, 24 of one or both of the fitting hole h1 and the socket angle h2 may also be angular and configured to make line contact with the fastening object Z.

In addition, while the above embodiment describes a method for reducing the weight of the socket 100, the target for weight reduction is not limited to the socket 100. It is also possible to reduce the weight of any cylindrical part that is provided with at least one of a fitting hole h1 or a drive angle h2, such as an extension bar, universal joint, or conversion adapter that constitutes the tightening tool 200.

Furthermore, while the tightening tool 200 in the above embodiment has a separate handle X and socket 100, the tightening tool 200 according to the present invention may have an integrated handle X and socket 100.

In addition, the tightening tool 200 may be a wrench. In this case, a fitting hole h1 that fits into the object to be tightened Z is formed at the tip, and this tip corresponds to the cylindrical portion referred to in the claims.

In the embodiments described so far, the socket has a regular shape along the circumferential direction (more specifically, a point-symmetric shape), and is designed so that the stress applied to the socket during operation is distributed to multiple points.
With this type of shape, if a large amount of stress is applied to the socket that causes it to break, it is impossible to predict which point it will break, and if it breaks in multiple places, there is a concern that fragments will fly around.

To ensure safe fracture, the socket 100 may have an irregular shape along the circumferential direction, as shown in Figures 13 to 15. More specifically, the socket 100 may be formed with one circumferential location formed as a stress concentration location SC where stress is more concentrated than in other locations.

This stress concentration point SC can be formed, for example, by making the distance between one vertex 13 of the fitting hole h1 and its corresponding point corresponding point 14 shorter than the distance between the other vertices 13 of the fitting hole h1 and their corresponding point corresponding points 14.

More specifically, in the configuration shown in FIG. 13, one second curved region S2 is recessed further toward the central axis than the other second curved regions S2.
As a result, the distance between the point corresponding location 14 set in one second curved region and the corresponding vertex 13 becomes shorter than the distance between the point corresponding location 14 set in another second curved region and the corresponding vertex 13.
As a result, a stress concentration point SC is formed between the point corresponding portion 14 set in one second curved region and the corresponding vertex portion 13 (the hatched portion in FIG. 13).

14, the center O1 of the fitting hole h1 is eccentric to the center O1' of the outer peripheral surface of the tip tube portion 10. A more specific embodiment is one in which the center O1 of the fitting hole h1 and the center O1' of the outer peripheral surface of the tip tube portion 10 are eccentric to move closer to one point corresponding location 14 from a state in which the center O1 of the fitting hole h1 and the center O1' of the outer peripheral surface of the tip tube portion 10 overlap each other.
As a result, the distance between one point corresponding portion 14 and the corresponding vertex 13 becomes shorter than the distance between the other point corresponding portion 14 and the corresponding vertex 13 .
As a result, a stress concentration point SC is formed between the one point corresponding portion 14 and the corresponding vertex portion 13 (the hatched portion in FIG. 14).

Furthermore, in the configuration shown in FIG. 15, one vertex 13 of the fitting hole h1 is recessed more than the other vertex 13.
As a result, the distance between this one vertex 13 and the corresponding point corresponding portion 14 becomes shorter than the distance between the other vertex 13 and the corresponding point corresponding portion 14 .
As a result, a stress concentration point SC is formed between the one vertex 13 and the corresponding point (the shaded area in FIG. 15).

Furthermore, although not shown, the stress concentration point SC may be formed, for example, by providing a groove or edge in one of the second curved regions on the outer peripheral surface of the tip tube portion 10.

The stress concentration point SC does not necessarily have to be provided in the distal end tubular portion 10 , but may be provided in the proximal end tubular portion 20 .
Furthermore, the stress concentration point SC does not necessarily have to be formed between one vertex portion 13 and the corresponding point corresponding point 14, but may be formed, for example, between one side portion 11 and the corresponding side corresponding point 12.

By forming the stress concentration point SC in this way, even if a large stress is applied to the socket 100, it will break from the stress concentration point SC, preventing fragments from flying off and allowing for safe breaking.

In addition, in the above embodiment, the various ridges formed on the outer surface of the socket 100, such as the ridge where the first curved region S1 and the second curved region S1 overlap and the ridge where the first curved region T1 and the second curved region T2 overlap, are steep, which can provide the effect of providing excellent grip.
On the other hand, in order to make the socket 100 soft to the touch, some or all of the above-mentioned ridges may be rounded.

It goes without saying that the present invention is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the invention.

200... Fastening tool 100... Socket Z... Fastening object X... Handle X1... Square drive h1... Fitting hole h2... Insertion angle h3... Communication hole 10... Tip tube portion 11... Side portion 12... Side corresponding portion 13... Vertex portion 14... Point corresponding portion C1... Circumscribed circle O1... Center M1... Center L1... First virtual line L2... First virtual line P1... Passing portion S1... First curved region S2... Second curved region 20... Base end tube portion 21... Side portion 22... Side corresponding portion 23... Vertex portion 24... Point corresponding portion C2... Circumscribed circle O2... Center M2... Center L3... Third virtual line L4... Fourth virtual line P2... Passing portion T1... First curved region T2... Second curved region T3... Bulging region 30... Lightening portion SC ...Stress concentration points

Claims (10)

A tightening tool having a tubular portion formed with a fitting hole that fits into an object to be tightened,
the tightening tool is a wrench or a wrench socket,
The fitting hole has a polygonal shape when viewed from the axial direction,
a side corresponding portion on the outer peripheral surface of the cylindrical portion that corresponds to the center of a side portion of the fitting hole and a point corresponding portion on the outer peripheral surface that corresponds to a vertex portion of the fitting hole are located radially inside of a circumscribed circle of the outer peripheral surface ,
The tightening tool is configured such that the points on the outer peripheral surface through which the circumscribed circle passes are located line-symmetrically with respect to each imaginary line connecting the center of the fitting hole and the point-corresponding location. A tightening tool having a cylindrical portion formed with an insertion angle into which a square drive of a handle gripped by an operator is inserted,
The fastening tool is a wrench socket, and a fitting hole that fits into an object to be fastened is formed on the opposite side of the drive angle of the cylindrical portion,
a side corresponding location corresponding to the center of a side of the insertion angle on the outer peripheral surface of the portion of the cylindrical portion where the insertion angle is formed , and a point corresponding location corresponding to a vertex of the insertion angle on the outer peripheral surface are located radially inside of a circumscribed circle of the outer peripheral surface,
The tightening tool is configured such that the points on the outer peripheral surface through which the circumscribed circle passes are located line-symmetrically with respect to each imaginary line connecting the center of the insertion angle and the point-corresponding location. A tightening tool as described in claim 1 or 2, wherein the radial thickness dimension at the point on the outer peripheral surface through which the circumscribed circle passes is greater than the radial thickness dimension at the edge-corresponding location and the radial thickness dimension at the point-corresponding location. The tightening tool according to claim 1 , wherein at least one of the side-corresponding portions and the point-corresponding portions is provided in a flat area on the outer circumferential surface that is parallel to the central axis. A tightening tool having a tubular portion formed with a fitting hole that fits into an object to be tightened,
the tightening tool is a wrench or a wrench socket,
The fitting hole has a polygonal shape when viewed from the axial direction,
a side corresponding portion on the outer peripheral surface of the cylindrical portion that corresponds to the center of a side portion of the fitting hole and a point corresponding portion on the outer peripheral surface that corresponds to a vertex portion of the fitting hole are located radially inside of a circumscribed circle of the outer peripheral surface,
At least one of the side-corresponding portions and the point-corresponding portions is provided in a curved region on the outer circumferential surface that curves toward the central axis. A tightening tool having a cylindrical portion formed with an insertion angle into which a square drive of a handle gripped by an operator is inserted,
The fastening tool is a wrench socket, and a fitting hole that fits into an object to be fastened is formed on the opposite side of the drive angle of the cylindrical portion,
a side corresponding location corresponding to the center of a side of the insertion angle on the outer peripheral surface of the portion of the cylindrical portion where the insertion angle is formed , and a point corresponding location corresponding to a vertex of the insertion angle on the outer peripheral surface are located radially inside of a circumscribed circle of the outer peripheral surface,
At least one of the side-corresponding portions and the point-corresponding portions is provided in a curved region on the outer circumferential surface that curves toward the central axis. A tightening tool having a tubular portion formed with a fitting hole that fits into an object to be tightened,
The fitting hole has a polygonal shape when viewed from the axial direction,
a side corresponding portion on the outer peripheral surface of the cylindrical portion that corresponds to the center of a side portion of the fitting hole and a point corresponding portion on the outer peripheral surface that corresponds to a vertex portion of the fitting hole are located radially inside of a circumscribed circle of the outer peripheral surface,
A tightening tool in which one location in the circumferential direction is formed as a stress concentration location where stress is concentrated more than other locations. A tightening tool as described in claim 7, wherein the stress concentration point is formed between one of the vertices of the fitting hole and the corresponding point. A tightening tool having a cylindrical portion formed with an insertion angle into which a square drive of a handle gripped by an operator is inserted,
a side corresponding location on the outer peripheral surface of the cylindrical portion that corresponds to the center of a side portion of the insertion angle and a point corresponding location on the outer peripheral surface that corresponds to a vertex portion of the insertion angle are located radially inside of a circumscribed circle of the outer peripheral surface,
A tightening tool in which one location in the circumferential direction is formed as a stress concentration location where stress is concentrated more than other locations. A tightening tool as described in claim 9, wherein the stress concentration point is formed between one of the vertices of the drive angle and the corresponding point.