To provide a screw part having a drive shape capable of preventing coming out of a tightening tool and transmitting a tightening stress efficiently, and also to provide the screw part tightening tool.
The drive shape 10 formed in a head part 3 of the screw part is formed by overhanging parts 12 like small leaves protruding radially apart from each other and from the center O of the head part at an equal angle, curved parts 13 recessed on inner sides, and drive walls 14 provided between the overhanging parts 12 and the curved parts 13. The direction C of the tightening stress applied on the drive wall 14 is substantially vertical for a straight line 7 passing through the center O of the head part and a vertex of the overhanging part. Or, the direction of the tightening stress applied on the drive wall is substantially vertical for a straight line passing through the center and the drive wall. Or, the drive wall is formed as two faces and the direction of the tightening stress applied on the drive wall is divided into two directions.
KATO ATSUSHI
TSUCHIYA YASUHIRO
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