Enduro Zero Ceramic Grade 3 6902 Sealed Cartridge Bearing 15 x 28 x 7mmEnduro Zero Ceramic Grade 3 6902 Sealed Cartridge Bearing 15 x 28 x 7mm. Zero Ceramic bearings are the ultimate race day weapon. Oversized Grade 3 balls roll on races which are ground to a mirror finish after receiving Magnetite and then Cryogenic treatments for hardness and longevity and slippery Silicone seals to produce minimum resistance. All measurements are in millimeters ABEC 5 precision cartridge bearing CERBEC USA Grade 3 Si3n4 Silicon