| 摘要 |
A drive hole (3) of a head part (2) of a fastening tool comprises an upright surface (3a) which constitutes a hexagon in plan view, an arc surface (3c) which has an arc connecting vertexes of the hexagon, a flank surface (3d) which is located between the upright surface (3a) and the arc surface (3c) and extends upward in a loosening direction from the bottom side of the upright surface (3a), and a step part (5) which restricts the dropping of a hexagon wrench. The step part (5) is provided at the position of a vertex angle of the hexagon in plan view, the vertex angle being formed by two adjacent upright surfaces (3a, 3a). Since an edge of the hexagon wrench rides on a crossing position (R1) of a side surface (5b), the upright surface (3a), and the flank surface (3d), the hexagon wrench does not drop to a bottom surface (3b). Therefore, at the time of loosening, the hexagon wrench is smoothly detached from the drive hole (3). |
