| 摘要 |
A reinforcement groove part is formed in one of the side wall parts in a manner so as to be depressed inward. The reinforcement groove part is formed in a manner such that, in a state where the center axis of a through hole formed in said one of the side wall parts matches the rotation axis of a take-up drum, a portion of the reinforcement groove part formed along a peripheral edge part of said through hole is located near a flange part. The projecting part of the reinforcement groove part projecting inward of said one of the side wall parts is formed in a manner so as to have substantially the same height as the axially inner surface of the flange part. The reinforcement groove part is formed along the peripheral edge part of the through hole and extends continuously from the peripheral edge part of the through hole and obliquely outward with respect to the radial direction. |
