| 摘要 |
PROBLEM TO BE SOLVED: To reduce the necessary driving torque for easier tightening work and increasing pull-out resistance. SOLUTION: In a screw threads comprising 1st ridge 6, circular in plan view and located on the side of head 3 of a shank 2, and 2nd ridge 7, non- circular in plan view and located on the side of 4 of the shank 2 and continuing to the 1st ridge 6; a root diameter D2 of the shank 2 in a region R2 containing the 2nd ridge 7 is smaller than a root diameter D1 of the shank 2 in a region R1 containing the 1st ridge 6, (D1>D2), and an included angleθ2 of the 2nd ridge 7, is smaller than thatθ1 of the 1st ridge 6, (θ1>θ2), and a cross-sectional area of the 2nd ridge 7 is smaller than that of the 1st ridge 6. |
