Patent attributes
A head portion includes an engaging portion capable of engaging with an engagement portion, a slit formed by cutting a part of a peripheral wall surface of the engaging portion, a protuberance which protrudes inward from the peripheral wall surface of the engaging portion, the protuberance including a slope the height of projection of which gradually increases along the circumference of the peripheral wall and which is oriented in a direction of rotation in a rotating operation, and a stop surface extending in radial directions of the engaging portion. The head portion includes an elastically deformable portion configured to cause at least one of two opposite side portions of the slit to be elastically deformed so that the slit is widened until a preset value is reached by the torque applied from the engaging portion to the engagement portion with the protuberance in mesh with an interlocking portion.
