FASTENING SCREW

摘要

PURPOSE: A fastening screw is provided to improving a tightening force because outer circumference of curved portion contacts tightening surface when tightening the screws and is not hanged to the tightening surface. CONSTITUTION: A fastening screw(101) comprises a head unit(102). A recess(120) is formed in center of the head unit. In seat surface of the head unit, a concave part(123) which interferes in the recess by remaining curved portion of outer circumference. The concave part is formed by inclined surface facing lower part of the recess. A seating surface(124) of the head unit is formed by soaring surface of the curved portion which soars from the lower part of the inclined surface. The seating surface of the head unit is installed in the inner side than the outer circumference. The seating surface of the head unit is installed in the inner side than top part of the outer circumference of the head unit.