Bearing Tolerance Standards
The tolerances for the boundary dimensions and running accuracy of rolling bearings are specified by ISO 492/199/582 (Accuracies of Rolling Bearings).

Regarding bearing accuracy classes, besides ISO normal accuracy, as accuracy improves there are Class 6X (for tapered roller bearings), Class 6, Class 5, Class 4, and Class 2, with Class 2 being the highest in ISO. The applicable accuracy classes and equivalents for each bearing type are shown in this section.