S608-2RS Ball Bearing Ultra-Light NYLON Cage ZrO2 Ceramic Balls Rubber Sealed 8mm x 22mm x 7mm S608-2RS Ball Bearing with Ceramic Balls with Rubber sealed and Nylon retainer inside them there are Zirconia fibers 7 Ceramic balls, 7 balls are made of Ceramic Zirconia fibers, each bearing has 2 Rubber seal to protect the bearing from dust or any possible contamination, this is self lubricated bearing.