| 摘要 |
<p>Modification to the shape of the head part (6) of a drilling screw resulting in an improved insertion performance of the drilling screw during a punching operation, a fastening performance of the drilling screw when seated as well as a finishing treatment upon completion of the fastening against a fastened member. The head part (6) comprises an upper large diameter part (13) formed with the first seat surface (12) of a frusto-conical shape whose outer circumference forms a curved concave surface and a small diameter part (15) forming a second seat surface (14) of a frusto-conical shape concentrically and integrally connected to a lower part of the large diameter part (13) and having its outer circumference formed as a curved concave surface, and an annular projecting edge (16) formed between the seated surfaces (12,14) of the two-stage curved concave surfaces. An outer circumference of the small diameter part (15) is provided with a plurality of slot facing projections (16) extending in a longitudinal direction along the curved concave surface of the second seat surface (14). <IMAGE></p> |
