Bearing internal clearance

Bearing internal clearance (fig 1) is defined as the total distance through which one bearing ring can be moved relative to the other in the radial direction (radial internal clearance) or in the axial direction (axial internal clearance).
It is necessary to distinguish between the internal clearance of a bearing before mounting and the internal clearance in a mounted bearing, which has reached its operating temperature (operational clearance). The initial internal clearance (before mounting) is greater than the operational clearance because different degrees of interference in the fits and differences in thermal expansion of the bearing rings and the associated components cause the rings to be expanded or compressed.
The radial internal clearance of a bearing is of considerable importance if satisfactory operation is to be obtained. As a general rule, ball bearings should always have an operational clearance that is virtually zero, or there may be a slight preload. Cylindrical, spherical and CARB toroidal roller bearings, on the other hand, should always have some residual clearance - however small - in operation. The same is true of tapered roller bearings, except in bearing arrangements where stiffness is desired, e.g. pinion bearing arrangements, where the bearings are mounted with a certain amount of preload, see section
The bearing internal clearance referred to as Normal has been selected so that a suitable operational clearance will be obtained when bearings are mounted with the fits usually recommended and operating conditions are normal. Where operating and mounting conditions differ from the normal, e.g. where interference fits are used for both bearing rings, unusual temperatures prevail etc., bearings with greater or smaller internal clearance than Normal are required. In such cases, SKF recommends checking residual clearance in the bearing after it has been mounted.
Bearings having an internal clearance other than Normal are identified by the suffixes C1 to C5.

SuffixRadial internal clearance
C1Less than C2
C2Less than Normal
CNNormal, only used in combination with letters indicating reduced or displaced clearance range
C3Greater than Normal
C4Greater than C3
C5Greater than C4
Tables providing the clearance values for the various bearing types can be found in the text preceding the relevant product section. For paired single row angular contact ball bearings and tapered roller bearings, double row angular contact ball bearings and four-point contact ball bearings, values for the axial internal clearance are provided instead of radial clearance, as the axial clearance is of greater importance in application design for these bearing types.
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