Bearing Size: 8mm x 22mm x 7mm (608) – Metal Shield – Ceramic Ball Bearing – 4 BEARINGS + 2 SPACERS – This is probably the best value for a ceramic bearing on the market. High precision tooling for less friction. The balls are made of Zirconium Oxide for ultimate durability with a nylon high speed ball retainer & 2 metal shields. The metal shields keep all dust and contaminates out, and the bearings are self lubricating so you never have to worry about servicing them! These ceramic bearings are lighter and faster than normal steel ball bearings and the oil-free raceway provides a longer running life.