S608-2RS Ball Bearings Sealed & Stainless Steel Ceramic Balls Si3N4 S608-2RS Ceramic is low friction 8mm axle skate bearings, bearings work in skateboards, longboards, inline skates, rollerblades and roller hockey, double sealed, radial and deep groove ball bearings, S608-2RS bearings are made of Stainless Steel with Si3N4 Ceramic (Silicon Nitride) balls, S608-2RS bearing are closed with seals to protect the bearing from dust or any possible contamination.