A ball bearing supports radial and axial loads, reducing rotational friction in the process. The most common type of ball bearing is the single row groove ball bearing, which features deep raceway grooves, with the inner and outer rings having a larger radius compared to the radius of the balls. Grooved ball bearings are rugged and suitable for very high speeds. Y-bearings or insert bearings feature a convex outer ring and often an extended inner ring. Angular contact ball bearings can accommodate radial and axial loads simultaneously. The raceways in inner and outer rings are displaced relative to each other, in the direction of the bearing axis. Self-aligning ball bearings generate less friction compared to other types of ball bearings, allowing them to remain cool even at high speeds. The size of ball bearings is determined by the size of the bore and the external diameter, with different sizes suiting different applications. Ball bearings have specific grades, ranging from 2,000 to 3, defining their geometric tolerances. The smaller the number, the higher the precision. The load rating makes explicit the capacity or the extent of load the ball bearing can support. Most ball bearings are made of chrome steel, though other materials such as carbon steel, brass, tungsten-carbide, titanium and even plastic are widely used.