Range of initial internal clearance
Bearing types for adjusted bearing arrangements – such as angular contact ball bearings, tapered roller bearings or spherical roller thrust bearings – have their internal clearance set during mounting. The internal clearance of such an arrangement, even though set by adjustment during mounting, will nevertheless have a range.
For other bearing types, the initial internal clearance is determined during their manufacture. ISO has defined five clearance classes for specifying the degree of initial internal clearance in a bearing (→ Internal clearance). Each clearance class represents a range of values. The size of the ranges varies depending on bearing type and size. Clearance class details are listed in relevant product sections.
Initial clearances greater than Normal, such as C3 or even C4 clearance classes, are very common today. This is because modern bearings take higher loads and require tighter interference fits, and typical operating conditions are different, compared to when the clearance classes were defined.
For universally matchable single row angular contact ball bearings and matched tapered roller bearings, double row angular contact ball bearings and fourpoint contact ball bearings, values for the axial internal clearance are given instead of radial internal clearance, because the axial clearance is of greater practical importance for these bearing types. Radial internal clearance is related to axial internal clearance and that relationship is determined by the bearing type and its internal geometry. More details are given in the product sections.