Thrust bearings include a broad range of bearings that accommodate axial loads. Also referred to as axial force, thrust is parallel to the axis of rotation. Depending on the application, there are many types and variations of thrust bearings. Ball thrust bearings effectively withstand pure thrust loads. The two rings, also called washers or washer seats, often feature grooves to allow for higher load capacities. Flat-race bearings typically have lower limiting speeds than grooved-race bearings. Ball thrust bearings are available in single- or dual-direction designs. Aligning seat washers correct initial assembly misalignments. Hydrodynamic thrust bearings act on pressurized fluid and facilitate motion in a wide range of heavy-duty industrial equipment. Fixed and tilting-pad hydrodynamic thrust bearings may be used in hydroelectric turbines and generators.