Ball bearings are the most common and most used type of bearing found in a number of objects (as shown in the figure below).

Also known as anti-friction bearings, ball bearings are small metallic or ceramic spheres used to reduce friction between axles and in numerous applications. These bearings are able to handle both thrust and radial loads and are used for applications where the load is relatively small. Load in a ball bearing is transmitted from the outer surface to the ball, and from the ball to the inner surface.

Since the ball is spherical in shape, it contacts the inner and outer race at a very small point, which helps it spin evenly and smoothly. But the contact area holding that load is very small, so if the bearing is overloaded then the balls can deform, ruining the bearing.