UCFA206 Black Oxide Plated Insert Bearing Adjustable Flange Cartridge Bearing Unit 30mm Mounted BearingsUCFA206 Black Oxide Plated Insert Bearing Adjustable Flange Cartridge Unit 30mm Inner Diameter UCFA206 Black Oxide Plated Insert Bearing Adjustable Flange Cartridge Unit, the inner Diameter is 30mm. Black oxide has certain properties and characteristics that makes it ideal for certain applications. It is used to add corrosion resistance and for appearance Item: UCFA206 Black Oxide Plated Insert Bearing + Flamge housing Type: Adjustable Flange