Ball Bearings 12x21x5 Stainless Steel Lot of 10 Bearings 10 Bearings Stainless Steel Ball Bearings , this is a popular size that could be used in many application that uses this size 12mm x 21mm x 5mm. Bearings are made of Stainless Steel and can rotate up to 39,000 rpm, each bearing has 2 Rubber Seal to protect the bearing from dust or any possible contamination, also bearings are pre-lubricated with grease.