| 摘要 |
A male screw 1 is divided along a partial length from the head 2 to a part of the shank 3 by a second groove 7 into at least two portions 11, 12. The portions 11, 12 divided by the second groove 7 have their outer peripheral surfaces extending obliquely so that a diameter of the male screw 1 reduces progressively downward from the head 2.
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