Timepiece wheel (1) overmoulded onto an arbour (2). The wheel is plastic injection overmoulded onto a washer (3) fitted onto said arbour (2). Said washer (3) is of lower density than that of said arbour (2).Said washer (3) includes at least one plane surface (4) forming a bearing and sealing surface (40) for cooperating in a sealed manner with an injection mould for the overmoulding operation.A particular version is an escape wheel whose teeth are formed during overmoulding onto said arbour (2) and said washer (3), and it includes an escape pinion (5) mounted in abutment on said washer (3) or integral with said washer (3).