A bearing is a machine element that constrains relative motion to only the desired motion, and reduces friction between moving parts. The design of the bearing may, for example, provide for free linear movement of the moving part or for free rotation around a fixed axis; or, it may prevent a motion by controlling the vectors of normal forces that bear on the moving parts. Many bearings also facilitate the desired motion as much as possible, such as by minimizing friction. Bearings are classified broadly according to the type of operation, the motions allowed, or to the directions of the loads (forces) applied to the partsDeep groove ball bearings are the most widely used roller bearing type in the world due to their versatility and overall performance. They are characterized by having deep raceway grooves in which the inner and outer rings have circular arcs of slightly larger radius than that of the balls. They also have non-separable rings. Their straight forward basic design has many advantanges.

Excellent for high speeds.
Good radial load capacity.
Acceptable axial load capacity in both directions.
Have low torque capacity at startup and running speeds.
Can operate with low noise.
Require little maintenance.

As flexible as the performance is, the configurations of single row ball bearnigs is also as versatile. These bearings often have steel shields or rubber seals installed on one or both sides and are pre-lubricated with grease. Also, snap rings are sometimes used on the outside edge. While many different retainers are available, pressed steel cages are most commonly used.