UC204-12-BLK Oxide Plated Plated Insert 3/4 Bore BearingUC204 12 BlacK Oxide Plated Insert Ball Bearing 3 4" inch Inner Diameter UC204 12 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