| 摘要 |
PROBLEM TO BE SOLVED: To prevent a come out phenomenon of a driver bit, and a conventional screw breakage by improving the constitution of a groove in a cross groove of a screw and improve work efficiency by always realizing appropriate and quick screw fastening operation even when breakage is caused in a part of the cross groove. SOLUTION: In the screw, screw heads 30a is provided with a bit fitting groove 32 constituted by the cross groove, inclined grooves are formed each of which is inclined by a predetermined amount from an edge of the bit fitting groove toward the center of a screw neck, and an approximately conical bottom face is formed at the center in which the inclined groove parts cross to each other. In this screw, the edge of the bit fitting groove 32 is formed as an approximately vertical edge wall 32a having a predetermined depth, each of the grooves 32b is formed so as to have an inclined angleβof about 45 deg. from each of lower edges 32a' of each of the edge walls toward the conical bottom face in the center of the screw neck part 30b, and the conical bottom face 34 is formed so as to have an inclined angleαof about 28 deg..
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