Like Ceramic Hybrid, Zero Ceramic use a combination of ceramic (Silicon Nitride - Si3n4) balls and steel races, except they are of higher Grade 3 quality. The races are also black oxide treated and ground to a mirror finish which prevents corrosion and provides near perfect efficiency and tolerances.Key Features: Bearing Code: 6805, Dimensions: 25 x 37 x 7mm, ABEC: 5, Grade: 3, Seals: VV, Grease: Kyodo Yushi PS-2, Application: Hubs, Bottom Brackets, Weight: 18.74g.