GB/T 307 and ISO 492 classify bearings from P0 (normal) to P2. P0 suits the vast majority of general machinery; P6 fits higher-speed or smoother-running positions; P5 serves machine-tool spindles and precision instruments; P4 and above are reserved for ultra-precision applications. Selection should follow speed, the role of the bearing position, and economics — each class raises manufacturing difficulty and cost significantly. Hengtuo supplies P0/P6/P5 as standard, with P4 available on precision double row cylindrical roller bearings, backed by roundness and roughness measurement reports.