UC203 17mm-BLK Oxide Plated Plated Insert 17mm Bore BearingUC203 17mm Black Oxide Plated Insert Ball Bearing 17mm Inner Diameter UC203 17mm BLK Oxide Plated Insert Ball Bearing, bearing is wide inner ring with spherical outer ring, bearing is relubrication groove with oil hole on set screw side, bearing is anti rotation pin on side opposite grease groove, bearing is nylon patched class 3A set screws. Black oxide has certain properties and characteristics that makes it ideal for certain applications. It is