Tolerance classes P0–P4

Tolerance classes define how precisely a bearing's bore, outside diameter, width and running accuracy are manufactured. ISO 492 grades them P0 (normal), P6, P5 and P4, with tolerances becoming finer in that order; P0 is not marked in the designation, higher grades appear as suffixes. The American ABEC scale corresponds approximately: ABEC 1 to P0, ABEC 3 to P6, ABEC 5 to P5, ABEC 7 to P4.

Finer classes improve runout and seat accuracy — essential for machine-tool spindles, metrology and high-speed applications — while P0 suffices for most general machinery. Note that tolerance class is independent of internal clearance; both must be matched when replacing a bearing.