Thrust ball bearings have actually balls confined in a cage between the shaft raceway washer that represents the inner ring, and the housing raceway washer that corresponds to the external ring. They can bear just single-direction axial loads.
The single-acting thrust ball bearing consists of a shaft washer, a housing washer and a ball set with cage. The double-acting type consists of a shaft washer (centre washer), two housing washers and two ball sets with cages. To compensate for misalignments of the shaft, bearings with spherical housing washers and assistance washers must be used.