Abstract: Provided is a brake disc having excellent cracking resistance. A brake disc 1 according to an aspect of the present invention comprises a plurality of drain recesses 3, each formed in an area against which a brake pad is abutted, wherein the angle of a shoulder portion 31 formed by a friction surface against which the brake pad is abutted and an inner peripheral surface of an opening of the drain recess 3 is an obtuse angle.

Abstract: A rotary member in the form of a sprocket or a brake disc for transmitting a drive force or brake force, the rotary member having an annular hub portion arranged on a center side, an annular ring portion arranged on an outer circumferential side, and a plurality of arm portions connecting the hub portion and the ring portion, with a plurality of weight reduction holes partitioned by the arm portions between the hub portion and the ring portion. The plurality of arm portions are provided so that centers of their distal end portions on the ring portion side and centers of their proximal end portions on the hub portion side are offset in one circumferential direction, respectively, and the hub portion and the ring portion are not directly connected to each other by longitudinal sectional lines that intersect with the arm portions in a radial direction of the rotary member.

Abstract: A sprocket made of low carbon steel of not more than 0.25 wt % in the carbon content comprising teeth portion which are quenched to a hardness close to the theoretical maximum quenching hardness of 35-55 Rockwell hardness C, and an inside diameter mounting hole.