tolérances

Tolérances, or tolerances in English, are the permissible deviation from a specified dimension or parameter in engineering and manufacturing. They define the range within which a part is considered acceptable and ensure interchangeability of components across suppliers and assemblies. Tolerances apply to linear dimensions, angular dimensions, and geometric characteristics, and may be bilateral (± a value) or unilateral (only above or below the nominal). For example, a shaft of 20.00 mm with a tolerance of +0.05/−0.00 is acceptable from 20.00 to 20.05 mm; a hole of 10.00 mm with +0.00/−0.05 accepts 9.95 to 10.00 mm.

Tolerances are often expressed using tolerance classes and fundamental deviations, as in ISO 286, or with geometric tolerancing using GD&T (ASME Y14.5/ISO 1101). Dimensional tolerances are complemented by geometric tolerances that control form, orientation, location, and runout, regardless of size. Tolerances influence fit: clearance, interference, or transition fits between mating parts.

Tolerance analysis considers production capability, cost, and functional requirements. Tolerance stack-up estimates predict how individual tolerances accumulate in assemblies. Measurement and verification use metrology tools such as calipers, micrometers, or coordinate measuring machines; statistical methods may be used to assess process capability.

In practice, tighter tolerances improve part interchangeability and function but raise cost and inspection burden. Standards and industry practices guide tolerance selection to balance manufacturability with performance.