... good quality 4,The materials are bearing steel Guanxian Aolong Precision Bearing ManufacturerThere are four parts of a bearing, they are:1,Inner and ... ,30300 series,32000 series,32200 series,32300 series.MaterialsCarbon steel,Stainless steel,Chrome Steel and Bearing steel,GCr-15Seals typeOpenPrecision rating P0Vibration LevelV1Tolerance CodeABEC-1Quality Standard ...