This type of bearings 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 an carry alternating axial load in either direction . Before using they have to be preloaded. 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 for machine tool spindles , while the single are used to support ball screws .