| 摘要 |
PROBLEM TO BE SOLVED: To provide a wood screw that can be easily screwed into a hard wood by a low torque, and have sufficient fastening force after screwing.SOLUTION: In a wood screw 1 having a tapered pointed end 4 at an extremity end of a cylindrical shank 3, a preceding screw thread 5 having a triangular section with a prescribed lead angle θ, a pitch P and a nominal diameter [d] is formed over a segment from the extremity end of the pointed end 4 to the extremity end of the shank 3, and a behind screw thread 7 having substantially the same lead angle θ, pitch P, nominal diameter [d] as those of the screw thread 5 and sectional shape is formed from a part near the extremity end of the shank 3 to an intermediate portion or a part near a rear end. The preceding screw thread 5 and the behind screw thread 7 are displaced to each other by a half pitch so as to form a double-start thread at the part near the extremity end of the shank 3 within a range of 1 pitch to 2 pitches.SELECTED DRAWING: Figure 1 |
