... . ceramic bearings2. Ball bearing.Roller bearing. Hub bearing 3.material,steel GCR - 15 ,ceramic4Quality authentication ISO 9001:2000 5.Hardness:62Greese ... ,51100,51200,51300,51400,DAC,BC, etc. Ring MaterialChrome Steel ,Carbon steel,Stainless steel Tolerance gradeGB/T307.1-205 ID Size 10mm~280mm ...