Patent ID: 7162939

Claim:
A tamperproof screw comprising: a screw head of said screw, inclined portions that have a specified angle of inclination and are formed toward a central portion of a neck portion of said screw from open end edge portions of bit engaging grooves, step portions that are respectively substantially perpendicular in cross section and are formed in intermediate point of said inclined portions, said step portions forming said bit engaging grooves in said screw, and a substantially conical bottom surface formed in the central portion where said inclined portions meet; said tamperproof screw being characterized in that: an inverted truncated cone shape hole portion that reaches said bottom surface is formed as a continuation, except for said step portions, of said inclined portions so that said open end edge portions of said bit engaging grooves take a maximum diameter of said inverted truncated cone shape hole portion, and a projecting portion is formed so as to protrude from a central portion of said bottom surface to a position above said step portions of said bit engaging grooves and below a top surface of said screw head.