To allow expansion

To provide clearance

To retain the abrasive

To permit minor adjustment

Annealing

Hardening

Tempering

Normalising

To add cutting ability

To relive strain and stress

To refine the grain structure

To regulate the hardness and toughness

To add cutting ability

To increase wear resistance

To relieve the internal stress

To refine the grain structure of the steel

To transmit torque

Assembly purpose

Lock the assembly part

Permit clearance between mating part