A bearing is a machine element that constrains relative motion to only the desired motion and reduces friction between moving parts.

The basic purpose of it are as follows:
• Guide the moving parts
• Reduce the friction
• Transmit the load

Bearings are made up of some common parts which are as follows:
1. Outer Ring
2. Inner Ring
3. Rolling elements
4. Cage
5. Seal

Bearings are classified broadly according to the type of operation, the motions allowed, or to the directions of the loads (forces) applied to the parts. Some of common types are as follows:
1. Deep Groove Ball Bearing
2. Angular Contact Ball Bearing
3. Self-aligning Ball Bearing
4. Cylindrical Roller Bearing
5. Tapered Roller Bearing
6. Spherical Roller Bearing
7. Needle Roller Bearing
8. Thrust Ball Bearing