PROBLEM TO BE SOLVED: To provide a screw part structure for a female screw and a male screw for achieving anti-loosening effect by combination of the female screw and the male screw.;SOLUTION: Of an inlet side end part and an outlet side end part of a screw part of the female screw, the outlet side end part is shrunk to be tapered along the whole circumference to have smaller inner diameter than a middle part to form the screw part, where threads of the female screw part with shrunk diameter are formed as irregularities repeatedly continuous in a circumferential direction. In trough bottoms of the screw part of the male screw to be engaged with the female screw, irregularities repeatedly continuous in a circumferential direction are formed. As the male screw is engaged with the female screw, at least one of projected parts in the threads of the female screw part with shrunk diameter is engaged with at least one of recesses in the trough bottoms of the male screw part of the male screw. The projected part of the female screw part with shrunk diameter bites the trough bottom of thread side surface of the male screw part to tighten them. Loosening between the male screw and the female screw can thus be prevented.;COPYRIGHT: (C)2004,JPO&NCIPI
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