The tolerances for the bore and outside diameters of rolling bearings are internationally standardized, see section Tolerances.
To achieve an interference or a clearance fit for bearings with a cylindrical bore and cylindrical outside diameter, suitable tolerance ranges for the seats on the shaft and in the housing bore are selected from the ISO tolerance system. Only a limited number of ISO tolerance grades need be considered for rolling bearing applications. The location of the most commonly used grades relative to the bearing bore and outside diameter tolerances are illustrated in fig 1.
Bearings with a tapered bore are mounted either directly on tapered shaft seats or on adapter or withdrawal sleeves, having an external taper, which are fitted to cylindrical shaft seats. In these cases, the fit of the bearing inner ring is not determined, as for bearings with a cylindrical bore, by the selected shaft tolerance but by the distance through which the ring is driven up on its tapered seat or sleeve. Special precautions with respect to the reduction of the internal clearance must be observed as mentioned in the sections Self-aligning ball bearings, Spherical roller bearings and CARB® toroidal roller bearings.
If the bearings are to be secured using adapter or withdrawal sleeves, larger diameter tolerances are permitted for the sleeve seat, but the tolerances for cylindricity must be tighter, see section Dimensional, form and running accuracy of bearing seats and abutments.
Tables with recommendations for fitsRecommendations for bearing fits for solid steel shafts can be found in:
Recommendations for bearing fits for cast iron and steel housings can be found in:
These recommendations for modern bearings are based on the general selection guidelines described above, developments in bearing design and years of experience for a very wide range of bearing arrangements and applications. Modern bearings can carry substantially greater loads than previous conventional bearings and the recommendations reflect these more demanding conditions. The tables of housing tolerance recommendations also provide information as to whether the outer ring can be axially displaced in the housing bore. Using this information it is possible to check whether the chosen tolerance is suitable for non-separable bearings that are to be used in the non-locating position and cannot accommodate axial displacement within the bearing.