Explain different types of fits in mechanical design and their applications?

Fits describe the relationship between mating parts. Clearance fits always have a gap (H7/g6), used for sliding or rotating parts. Interference fits always have overlap (H7/p6), used for press-fit assemblies requiring high torque transmission. Transition fits may have either clearance or interference (H7/k6), used for accurate location with possible assembly/disassembly. The ISO system uses hole basis (H) or shaft basis specifications with tolerance grades (IT6, IT7) defining precision levels.