A timepiece wheel overmolded onto an arbor. The wheel is plastic injection overmolded onto a washer fitted onto the arbor. This washer has a lower density than the arbor. This washer includes at least one plane surface forming a bearing and sealing surface for cooperating in a sealed manner with an injection mold for the overmolding operation. The timepiece wheel may be an escape wheel whose teeth are formed during overmolding onto the arbor and the washer, and it includes an escape pinion mounted and abutted to the washer or integral with the washer.