15267-2RS Sealed Ball Bearing with Si3N4 Ceramic Balls Silicon Nitride 15mm x 26mm x 7mm Made for bicycles 15267-2RS Sealed Ball Bearing with Si3N4 Ceramic Balls, bearing is made of Chrome Steel with Ceramic Balls (Si3N4),15267-2RS bearing is closed with rubber seals to protect the bearing from dust or any possible contamination,bearing is sealed and self lubricated,15267-2RS bearing is lubricated with grease.