A. Bearings Funtion
Bearings are accessories to support shaft, they can guide the circumgyration of shaft, support the accessory which racing on the shaft, bearings can be divided into rolling bearings and gliding bearings, bearings normally referred to are rolling bearings.

B. Rolling Bearing Definition
Rolling bearing is a kind of precise mechanical accessory, changing the sliding friction into rolling friction, to reduce friction loss.

C. Rolling Bearings Features
Advantages,
1, Less friction, less power loss, higher mechanical efficency.
2, Sizes are standardized, having interchange ability, assembly and dismantlement are very easy.
3, Structure is compact, with less weight, axial size is far more less.
4, With higher precision and rotating speed, longer use life.
5, Some kinds of bearings have self-aligning ability.
6, They are suitable to vast batches of production, with steady quality and high production efficiency.
Shortcomings,
1, Much noise.
2, the structure of bearing housing is more complex.
3, The cost is higher.

D. Rolling Bearings Fundamental Structure
Rolling bearing consists of inner ring, outer ring, rolling elements and retainers, the function of inner ring is to fit with shaft and rotate with it. The function of outer ring is to fit with bearing housing. Rolling elements take an action of support, depending on retainer, uniformly lay between the outer ring and inner ring, the size and quantity of rolling elements affect use capability and use life directly. Retainer can make rolling elements lay uniformly and prevent them from escaping, guide them to rotate, and take an action of lubrication.

E. Common Nomenclatures on Structure of Rolling Bearing Parts
     I.D (d): Iinner ring bore diameter.
   O.D (D): Outer ring diameter.
I.O.D(d2): Outside surface max. diameter of inner ring.
O.I.D(D2): Inner surface min. diameter of outer ring. 
         (X): Width of inner ring. 
         (B): Width of outer ring.
　　 (di ): Inner ring raceway Diameter.
　    (Di ): Outer ring raceway diameter.
　　   (r): Chamfer semidiameter.

F. Bearings Classification
In terms of the direction of load
Radial bearings and thrust bearings.
In terms of the kinds of the rolling parts
Ball bearings and roller bearings.
In terms of whether bearing can self-align or not when working
Rigid bearings and self-aligning bearings.
In terms of the sizes of diameter of bearing outer ring
Miniature bearings D< 26mm, Small bearing 26<D< 60mm, 
Medium and small bearings 60<D< <BR 120mm, Medium and large bearings 120<D< 200mm,  >Large bearings 200<D< <BR bearings   440mm, Super 440<D< 2000mm,>Massive bearings D> 2000mm.
In terms of usage
Railway bearings,
Automobile bearings,
Machine tool bearings,
Aviation engine bearings,
Electromotor bearings.
In terms of usage features
High temperature bearings,
Low temperature bearings,
High speed bearings,
Vacuum bearings,
Antimagnetic bearings,
Anti-corrosion bearings.
In terms of direction of load, nominal contact angle and sorts of rolling elements
Deep groove ball bearings,
Cylindrical roller bearings,
Needle bearings,
Spherical roller bearings,
Angular contact ball bearings,
Thrust angular contact ball bearings,
Thrust spherical roller bearings,
Thrust tapered roller bearings.

G. Rolling Bearings Code
Rolling bearing code is to show features, such as, rolling bearing, structure of parts, size, tolerance grade, technical characteristics, it consists of prepositive code, fundamental code, suffixes, details refer to Engineering and Technology.