The tolerances for the bore and outside diameter of rolling bearings are standardized internationally (→ Tolerances).
To achieve an interference or loose fit for metric bearings with a cylindrical bore and outside surface, suitable tolerance classes for the bearing seat on the shaft and in the housing bore are selected from the ISO tolerance system. Only a limited number of ISO tolerance classes need be considered for the shaft and housing seats for rolling bearings. The location of the most commonly used tolerance classes relative to the bearing bore and outside diameter surface are shown in fig. 1 (valid for bearings with Normal tolerances).
Each ISO tolerance class is identified by a letter and a number. The letter, lower case for shaft diameters and upper case for housing bores, locates the tolerance zone relative to the nominal dimension. The number indicates the range of the tolerance zone. The higher the number, the larger the tolerance zone.
Recommendations for bearing fits for solid steel shafts are provided in the tables referenced in the following:
- radial bearings with a cylindrical bore (table 1)
- thrust bearings (table 2)
These recommendations are based on the general selection guidelines described above, which take developments in bearing and housing materials, design and manufacturing into account. Modern bearings and housings can accommodate substantially heavier loads than was previously possible. The recommendations given here reflect these improvements.
All ISO tolerance classes are valid with the envelope requirement (such as H7) in accordance with ISO 14405-1:2010. For practical reasons, this is not indicated in the tables.
ISO 14405-1:2010 offers more possibilities to specify fits. For additional information, contact the SKF application engineering service.
Stainless steel bearings or shafts
The recommended fits in table 1, table 2, table 3 and table 4 can be used for stainless steel bearings. However, footnote 3 in table 1 does not apply, because stainless steel has a much higher coefficient of thermal expansion than standard steel. If tighter fits than those recommended in table 1 are needed, contact the SKF application engineering service. It may also be necessary to consider the initial bearing clearance, such as when using stainless steel shafts at elevated temperatures (→ Bearing internal clearance).