Ceramic Hybrid bearings feature ABEC-5 tolerances and premium features such as LLB seals, Graphite Nylon retainers, Silicon Nitride Grade 5 balls, and cryogenically treated steel races. ABEC 5 precision cartridge bearing Grade 5 Si3N4 Silicon Nitride balls 52100 high carbon Chromium alloy races Races receive 3 cryogenic treatments "LLB" type 2-lip low-contact Nitrile Butadiene rubber labyrinth seals Nylon/graphite retainer Bearing I.D. (mm): 30 mm Thickness: 7 mm Bearing O.D. (mm): 42 mm