S693-2RS Sealed Ball Bearing ABEC-5 Quality with Si3N4 Ceramic Balls Silicon Nitride 3mm x 8mm x 4mm S693-2RS is sealed ABEC-5 ball bearing, S693-2RS 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, S693-2RS bearing is sealed and self lubricated,the quality is set to EMQ (ABEC-5 quality) to ensure high speed, S693-2RS bearing is lubricated with grease.