The precision of bearing contains precision and rotating accuaracy dimension precision is a project that mount on shafts, it includes inside diameter, outside diameter, width, chamfer size tolerance or allowed value.Geometric accuracy includ diameter deviation, average inner diameter deviation, out side diameter deviation, average diameter ring width deviation in single radial plane.rotation accuracy is rotating Pendulum, including the inner ring and outer ring radial swing and the axial runout, Side of inner ring and outer diameter surface perpendicularity tolerance range.Bearing precision grade from general grade 0 to 6, 5, grade 4 and grade 2, in turn, below is table comparison between preeision class of china GB 307 and other precision standard.Giant bearing precision grade is from grade 6, 5, 4 and 2 levels of four grades. 

The outer ring 11, the inner ring 12, and the ball 13 which are bearing components are 0.95 mass% or more and 1.10 mass% or less carbon, 0.05 mass% or more and less than 0.3 mass% silicon, 0.10 mass% or more and 0.50 mass% 11 A of outer ring raceways and 12 A of inner ring raceways which are the surface which consists of steel which consists of the following manganese, 1.30 mass% or more, and 2.00 mass% or less, and consists of steel which consists of remainder iron and an impurity, and contacts with other components. And the average nitrogen concentration in the surface layer regions 11B, 12B, and 13B which are regions within a depth of 20 μm from the ball rolling surface 13A are 0.2% by mass or more and 0.7% by mass or less, and in the surface layer regions 11B, 12B, 13B, 5 or more carbides with a diameter of 0.5 micrometer or less exist per 100 micrometer.