Self-aligning ball bearing has a spherical raceway in the outer ring and a double-raceway in the inner ring. This feature gives the bearings the self-aligning property, which can keep the machine operating well even when angular misalignment of the shaft relative to the housing occurs. Values of permissible misalignment errors of double row self-aligning ball bearings are given in the section “selection of bearing type”. The self-aligning ball bearing is mainly used to carry radial loads and light axial loads, but they can not carry pure axial loads.