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Tolerances control the dimensional accuracy of a bearing. We use ISO bearing tolerances which start at P0 and then move upwards in precision grade to P6, P5 and then P4. ISO tolerances are measured in thousandths of a millimetre (or microns). AFBMA (ABEC) bearing tolerances are also commonly used and these are measured in ten-thousandths of an inch starting at Abec1 then upwards to Abec3, Abec5 and Abec7. Confusingly there are slightly different Abec tolerance grades for instrument bearings (Abec1P, Abec3P, Abec5P, Abec7P) and for thin-section bearings (Abec5T, Abec7T).

Tolerances have no effect on radial play although it is sometimes mistakenly thought that improving the tolerances will produce a bearing with less play. Assuming that the shaft and housing are manufactured to the same tolerances as the bearing, higher bearing tolerances will produce better mating between shaft/housing and bearing, lower noise and vibration due to improved roundness and lower starting and running torque (also subject to radial play and lubricant).

For exact tolerance limits, please view our Tolerance Tables

If you always wondered exactly what measurements are checked, see Bearing Tolerances Explained

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Ball Bearing Tolerances