Ball bearings are a type of rolling-element bearing commonly used in various mechanical applications to reduce friction and support radial and axial loads. They consist of several key components, including:

1. Outer Ring: The outer ring is typically a stationary component that provides a housing for the ball bearings. It can be mounted or secured to the surrounding structure.
2. Inner Ring: The inner ring is the rotating component that the shaft or axle runs through. It is usually mounted on the rotating part of the machine.
3. Balls: Ball bearings get their name from the small, spherical balls that are positioned between the inner and outer rings. These balls are responsible for carrying the load and facilitating smooth rotation. They come in various materials, such as steel, ceramic, and plastic.
4. Cage or Retainer: The cage or retainer holds the balls in place and maintains an equal distance between them. It prevents the balls from coming into direct contact with each other, which could cause friction and wear.

Ball bearings work on the principle of rolling friction, which is significantly less than sliding friction. When a load is applied, the balls within the bearing rotate, reducing friction and enabling the smooth movement of the inner ring relative to the outer ring. This is why ball bearings are widely used in various applications, such as automotive wheels, industrial machinery, household appliances, and more.

Different types of ball bearings exist to accommodate various loads, speeds, and conditions, including deep groove ball bearings, angular contact ball bearings, thrust ball bearings, and self-aligning ball bearings. The choice of the right type of ball bearing depends on the specific requirements of the application.