SR8-2RS Sealed Ball Bearing ABEC-5 Quality with Si3N4 Ceramic Balls (Silicon Nitride) 1/2" x 1 1/8" x 5/16" Inch SR8-2RS Bearing is double sealed, radial and deep groove ball bearing,SR8-2RS bearing is made of Stainless Steel with Ceramic Balls (Si3N4) and Stainless steel cage,bearing is closed with rubber seals to protect the bearing from dust or any possible contamination,SR8-2RS bearing is sealed and self lubricated,SR8-2RS bearing is lubricated with grease.