UC205 25mm black Oxide Plated Plated Insert 25mm Bore BearingUC205 25mm Black Oxide Plated Insert Ball Bearing 25mm Inner Diameter UC205 25mm Black Oxide Plated Insert Ball Bearing, bearing is wide inner ring with spherical outer ring, bearing is re lubrication 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