Rolling the diameter makes it possible to replace grinding when this is made unfeasible by the small size of the pieces to be machined. In this case, the tolerance level is measured in microns.
In turn, lapping the ends involves finishing the surface by rubbing it with an abrasive until it reaches its correct dimensions. Mastered to perfection, this technique makes it possible to obtain two parallel, plane faces with an outstanding, surface finish, moreover, precision here is of the order of 15 microns.