| 摘要 |
<p>A groove (42) in which an inside diameter finishing tooth (40) is provided is located in the center of roll off (22) at three points between a plurality of rows of protrusions (20a-20f) in the chamfer (24) around the central axis (O), and the inside diameter finishing tooth (40) is provided at a position shifted by a predetermined angle (?) in the rotational direction (A) of a tap from the protrusions (20a, 20c, 20e) in the chamfer (24) at the edge of opening of the groove (42) on the side opposite to the rotational direction (A) of the tap. Consequently, an internally threaded screw (54) can be formed by plastically deforming the inner circumferential surface (52) of a prepared hole by using the plurality of rows of protrusions (20a-20f) in the chamfer (24) entirely, and the number of the protrusions (20a-20f) pertaining to thread formation of the internally threaded screw (54) increases. Since the load (deformation margin of plastic deformation) per one protrusion (20a-20f) decreases, excellent durability can be attained without increasing the axial dimension of the chamfer (24).</p> |
