This Ceramic-Hybrid Radial Bottom Bracket Bearing boasts 52100 high-Carbon Chromium alloy races paired with Grade 5 Silicon-Nitride Ceramic balls, filled to 90% with high-pressure, water-proof grease. The ceramic balls minimize wear and enhance bearing life by avoiding steel-on-steel contact. Typically, it serves as a direct replacement for Shimano external cup BBs using the plastic Shimano bearing insert. For those who prefer to bypass the plastic insert, the MR 2437 is the suitable alternative.