S61902-2RS ABEC-3 Stainless Steel Ball Bearing with Ceramic Balls (Si3N4 Silicon Nitride) S61902-2RS ABEC-3 Stainless Steel Ball Bearing, it has Ceramic Balls (Si3N4 Silicon Nitride), each bearing has 2 Rubber Seals to protect the bearing from dust or any possible contamination, also bearing is pre-lubricated with grease.