Bearing UCP211-34 2-1/8" Black Oxide Plated Insert Pillow Block Mounted BearingUCP211 34 Black Oxide Plated Insert Pillow Block Bearing 2 1 8" Inner Diameter Bearing This is the most common type of mounted ball unit. Black oxide has certain properties and characteristics that makes it ideal for certain applications. It is used to add corrosion resistance and for appearance. UCP211 34 2 1 8" Black Oxide Plated Insert Mounted Ball Bearing Shaft Dia: 2 1 8" inch Bolt Size: 5 8" inch Bearing No: UC211 34 Black Basic Load (Cr): 43. 4