Combination of screw with stabilized strength and screwdriver bit, and header punch for manufacturing the screw with stabilized strength

Abstract

A screw having stabilized strength, combination with a driver bit that best fits the screw, and a header punch for producing the screw. The screw having stabilized strength has letter Y-shaped bit-fitting grooves formed in the head portion of the screw. Forming the grooves makes fitting of a corresponding driver to the screw easy, prevents occurrence of a cam-out phenomenon to enhance work efficiency, makes torque transmission to be made smoothly and sufficiently, and stabilizes strength. The bit-fitting grooves are formed in a letter Y shape that is substantially equally divided into three sections in the circumferential direction, the grooves being formed at positions required distances away from the central portion of the screw head. The width of each of the grooves extending in radial directions from the central portion of the bit-fitting grooves is set so that the grooves are gradually expanded and substantially equally spaced with spacing each equal to the width of a boundary section between adjacent grooves. Further, the outer peripheral end wall surface of each bit-fitting groove is made substantially vertical from an opening edge section up to a required depth. The outer peripheral end wall surface is displaced downward from a lower edge section of the wall surface toward the central portion of the screw head, and the center where the wall surfaces meet are formed as a substantially conical bottom surface.