Abstract: A is attached to a hollow portion in a wheel, an inner peripheral groove is provided on an inner peripheral surface of the hollow portion and an outer peripheral groove is provided on the outer peripheral surface of the cap, forming a single annular space. Into the annular space a C-spring or an O-ring is inserted, thereby attaching the cap to the wheel. Further, the O-ring is sandwiched between the annular surface of the wheel and the inner surface of the cap, or magnets are sandwiched therebetween, for eliminating rattling.

Abstract: A cap 2 or 4 that can be easily attached to and removed from a wheel has no weak parts susceptible to breakage. The cap 2 or 4 is attached to a hollow portion 1f in the wheel 1, an inner peripheral groove 1e being provided on an inner peripheral surface 1c of the hollow portion 1f and an outer peripheral groove 2e being provided on the outer peripheral surface 2c of the cap, thus forming a single annular space. Into such annular space a C-spring 3 or an O-ring 5 is inserted, thereby attaching the cap 2 or 4 to the wheel 1. Further, an O-ring 5 may be sandwiched between the annular surface 1d of the wheel 1 and the inner surface 2d of the cap 2, or magnets 6a and 6b may be sandwiched therebetween, and rattling is eliminated.