| 摘要 |
Modification of the shape of a head part of a drilling screw resulting in an improved inserting performance when a punching operation is carried out, a fastening performance when the screw is seated, and a finishing process upon completion of fastening against a fastened member. A seat (12) of the head part (6) has a frusto-conical surface, the outer circumference of the seat (12) being a curved concave surface. The upper surface (9) of the head part (6) is formed into a spherical concave surface. The head part (6) is provided with a plurality of slot facing projections (15) extending from the small diameter part (11b) at a lower portion of the head part (6) adjacent to a threaded shank part (4) of the screw along the curved concave surface of the seat surface (12) in a longitudinal direction. The upper surface (9) of the head part formed with a spherical concave surface is provided with chamfered portions (13) in which an opening edge of the engaging groove (10) of a cross-shaped hole is cut in a conical shape. <IMAGE>
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