Build simple, affordable linear motion systems with these wheel kits. Each kit contains: (1) polycarbonate solid wheel; (2) 625-2RS ball bearings; (2) 1mmx5mmx10mm precision shim; (1) M5 nylon lock nut. The v-shaped wheels ride smoothly in v-slotted extrusions such as Openbuilds V-Slot(TM) or C-Beam(TM). Polycarbonate wheels offer greater resistance to wear and compression than typical delrin wheels. Note: the opening on the wheel that accepts the bearing is slightly undersized, making it difficult to set the bearings by hand; however, once the bearings are set by a press or simple woodworking clamp, the fit is much more secure.