PISTON FOR DISK BRAKE

PURPOSE:To prevent thermal deterioration of seal and boot materials while obtaining a thin-wall piston having sufficient strength by constructing said piston with two parts consisting of a head-part body and a sliding outer cylinder part so as to prevent frictional heat generated in a friction pad from being conducted to the entire piston. CONSTITUTION:A sliding outer cylinder 10 which has a round projecting part 8 on its bottom center and a boot groove 9 for installing a boot 7 and provided on the end of the opening on the other side, and a cylindrical head-part body 12 which has flanged head 11 for pressing a friction pad 2 and an opening on the other end, are fixed to each other, with a gap provided between the bottom surface of the flange of the head 11 and the end of the opening of the sliding outer cylinder 10, thus a piston is formed. Since the strength of the bottom surface of the piston, i.e., the bottom surface of the sliding outer cylinder is being reinforced in such a form that the head-part body functions as reinforcing ribs, the bottom surface can be made thinner, thereby enabling the thinning of the sliding outer cylinder part as a whole and enabling production using a plate material.