thrust ball bearings , this type of bearing is separable , which can only carry axial load. The single direction bearings of them can only carry axial load in one direction .while the double carry alternation axial load in either direction. Before using they have to be perloaded. The thrust ball bearings are used in lathe centers. automobile clutches, reducers and so on. The double direction angular contact  thrust ball bearings are suitable fror machine tool spindles. while the single are used to support ball screws.

51100.51200.51300.51400.52200.52300 series