In the male screw body, a male screw side cooperation region having a non-circular cross section when viewed from the axial direction is formed in the shaft portion. The washer (cooperating member) engages with the male screw side cooperating region in the circumferential direction with the through hole as a non-circular shape. Further, the washer is provided with an engagement mechanism that engages with the female screw body in the circumferential direction. By doing in this way, rotation of the screw body in a specific direction is reliably prevented with a simple structure.
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