| 摘要 |
PROBLEM TO BE SOLVED: To prevent the slipping-off of an expansible screw to a side from a part between expansible legs and to improve the weak torsional rigidity providing the elastic rotation of a tip part of an expansible plug to a rear end part of the expansible plug. SOLUTION: A plurality of expansible legs 18 are connected to each other in the circumferential direction by an expansible material 22, and the expansible material 22 is provided with a number of spirally arranged slits 24.
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