7 Ball Black Ceramic Bearings-Silicon Nitride CeramicExtra Hard, High Density Black Ceramic Balls-Lighter than SteelCorrosion Resistant, Waterproof BallsRemovable Rubber Shield for Easy CleaningNylon Ball Retainer with Grease/Oil Mix for Speed & LongevityCeramic does not break down like steel thus eliminating steel debris that normally lead to bearing breakdownCeramic balls actually keep the steel races clean due to their extra hard properties by crushing debris and continually polishing the races