Roller thrust bearings carry pure thrust, or axial, loads with little or no radial forces. They use barrel-shaped rolling elements to carry single- or double-direction thrust loads. These rollers have a length perpendicular to the shaft and have different shapes that affect the bearing's efficiency. The two rings on roller thrust bearings, called washers, are also configured with different shapes and designs. They can be flat, grooved, tapered, concave, convex, or grooved. There are several different types of roller thrust bearings. Cylindrical roller thrust bearings contain slightly crowned rollers that work well in one-direction thrust applications. Needle roller thrust bearings contain long, thin cylindrical rollers in a spoke-like configuration. Tapered roller thrust bearings contain conical rollers for single- or double-direction thrust loads. A tapered raceway matches each side of the rollers for smooth rolling motion. Spherical roller thrust bearings contain contoured rollers arranged in a steep, angular position. Spherical roller thrust bearings are self-aligning and capable of accommodating shaft misalignment.