Roller bearings and ball bearings are two of the most common types of bearings. Roller bearings have high load bearing capacity and are used in large motors with heavy rotors. Smaller sized motors use ball bearings.
In case of very large motors, shell bearings are used. Grease is used as the lubricant in case of roller and ball bearings.
For Shell bearings, lube oil is used as the lubricant.
The bearings are usually designed to withstand radial loads. However, in some applications such as in the use of gears and belts, the motor may also be subjected to axial loads. In such cases, bearings such as angular ball bearings which can withstand axial loads can be used.