Bearings extend the working life of wheels, pulleys, and other rotating parts by reducing friction and enabling parts to move smoothly. Also called slewing rings or slewing bearings, they are installed between two surfaces to keep parts aligned and support axial and radial loads. Axial (thrust) bearings support loads parallel to the axis of the shaft, such as those exerted by a table supporting a weight. Radial bearings support rotating wheels and other applications where the force of the load is perpendicular to the shaft. Ball bearings are used with applications that have high axial loads and low-to-moderate radial loads. Mounted bearings (bearing units) have a bearing inside a housing unit to ensure a secure fit and mount. Sleeve and clip bearings support high loads, have no moving parts, and require lubricant to allow the shaft to turn smoothly. Spherical bearings and spherical rod ends are used on articulating joints and when the bearing must accommodate for axial misalignment.