| 摘要 |
PROBLEM TO BE SOLVED: To effectively prevent the occurrence of come out phenomenon of a driver bit through improvement of constitution of a polygonal hole of a screw head part, to prevent the occurrence of breakage of a screw like a conventional case, to achieve a constantly proper rapid screw fastening work, and to remarkably improve working efficiency. SOLUTION: A polygonal hole 32 consisting of approximately vertical wall surfaces 33 is formed down to a given depth in the central part of a screw head part 30a and a conical bottom surface pointing from the lower edge part of the vertical wall surface 33 toward the central part of a screw neck part is formed. In a so formed a screw 30 with a polygonal hole, a vertical stepped part 34 to form a polygonal inscribing circle is formed in the lower edge part 33a of the vertical wall surface 33 of the polygonal hole 32 formed in the screw neck part 30a. A conical bottom 35 pointing from the lower edge part 34a of the vertical stepped part 34 toward the central part of the screw neck part 30b is formed. |
