By minimizing friction and allowing parts to move smoothly, bearings improve the life of wheels, pulleys, and other rotating parts. They're also known as slewing rings or slewing bearings, and they're used to maintain parts aligned and support axial and radial stresses. Axial (thrust) bearings are used to handle loads that are parallel to the shaft's axis, such as those applied by a table supporting a weight. Radial bearings are used to sustain rotating wheels and other loads that are perpendicular to the shaft. Ball bearings are employed in applications where the axial load is strong and the radial load is low to moderate. To guarantee a secure fit and mount, mounted bearings (bearing units) have a bearing inside a housing unit. Sleeve and clip bearings are high-load bearings with no moving parts that require lubrication to allow the shaft to spin smoothly. On articulating joints and where the bearing must allow for axial misalignment, spherical bearings and spherical rod ends are employed.