| 摘要 |
Outer peripheral ends of torque transmitting section (20) of fitting projections (16) are made to contact with the side wall surfaces of torque transmitting sections (18) of recesses (12), and tightening torque is transmitted to a screw (10) through force application points (Q) which are the portions of the contact. In this process, in an end surface shape perpendicular to the center line (O1) of a recess (12) including a force application point (Q), the driving angle (¸) of a force (F) perpendicular to the surface is 0° or less. Therefore, the force (F) perpendicular to the surface is applied to the side wall of the recess (12) in a tangential direction about the center axis (O1) or in an inward direction. In comparison with a conventional case in which the force (F) perpendicular to the surface acts outwardly (0°<¸), a cam-out effect causing a screw tightening tool (14) to be dislodged from the recess (12) is less likely to occur. As a result, deformation of the recesses (12) and damage to or wear of the fitting projections (16) are suppressed, and the screw (10) can be considerably easily tightened with large tightening torque. |
