Abstract: A wheel part includes: a body having an axis; an annular outer surface through which the axis extends centrally and defining a socket; a stamp mounted in the socket for movement between an extended position wherein the stamp projects radially beyond the surface and a retracted position wherein the stamp terminates radially inwardly beneath the surface; and a bias mechanism adapted to bias the stamp for movement to the extended position. A manually grippable handpiece is adapted to releasably receive the body for rotatable movement about the axis and is adapted such that at least a portion of the surface projects beyond the housing. An inker is mounted to the handpiece in spaced relation to the surface such that, on rotation of the wheel, the stamp engages the inker and receives ink therefrom, whereby, when the body is roiled along a workpiece, the workpiece is demarcated at uniform intervals.