UCFA204-12 3/4" Black Oxide Plated Insert Bearing + Flange Cartridge Bearing Unit Mounted BearingUCFA204 12 Black Oxide Plated Insert Bearing + Flange Cartridge Unit 3 4" Inner Diameter Bearing UCFA204 12 Black Oxide Plated Insert Bearing + Flange Cartridge Unit, the inner Diameter is 3 4" inch. Black oxide has certain properties and characteristics that makes it ideal for certain applications. It is used to add corrosion resistance and for appearance UCFA204 12 Bearing Flange Cartridge Unit Basic Load (Cr): 12. 8 KN Basic Load (Cor): 6. 65 KN