S6902-2RS ABEC-3 Ball Bearing Stainless Steel and Ceramic Balls Si3N4 Silicon Nitride 15mm x 28mm x 7mm S6902-2RS Stainless Steel Ceramic Balls ABEC-3 quality Ball Bearing, each bearing has 2 Rubber Seals to protect the bearing from dust or any possible contamination, also bearing is pre-lubricated with grease.