Rotation transmission disc

A rotation transmission disc comprising:

• an outer circumferential portion on which a load acts when rotation is transmitted;
• a center opening portion formed inside the outer circumferential portion;
• and
• a plurality of attachment holes formed at positions projecting from the outer circumferential portion to an inside of the center opening portion for attachment of the rotation transmission disc to a rotating element,
• wherein a first crosspiece portion and a second crosspiece portion are formed in respective ranges of divided angles each of which is formed by any two adjacent attachment holes with respect to a center of the rotation transmission disc, the first crosspiece portion extending from a load point, which is an intersection between an internally dividing straight line extending in a radial direction to internally divide the divided angle at a predetermined angular ratio and an inner circumferential line with one radius inside a radius region of the outer circumferential portion adapted such that the load is applied, to one of the attachment holes forming the divided angle, the second crosspiece portion extending from the load point to the other attachment hole of the attachment holes forming the divided angle,
• the first crosspiece portion and the second crosspiece portion inside a range of an adjacent divided angle intersect one another, and each of the attachment holes is located in an intersecting region,
• wherein the rotation transmission disc is a sprocket, and
• wherein the predetermined angular ratio is 1:2 to 1:4.