Thrust ball bearings cannot withstand any radial loads; instead, they are made to withstand axial (thrust) stresses at high velocities. The balls in these bearings move within the raceway grooves on the bearing washers. Thrust ball bearings can be either single-direction or double-direction, and their shapes determine which types are called "flat seat" or "aligning seat." Seat washers that are spherical and aligned aid in providing mounting error tolerance.