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Calculators / ISO 286 fits

Calculators

ISO 286 fits

Find the limits of a hole and a shaft, such as Ø25 H7/g6, with the clearance or interference.

Hole
Shaft
Hole—
Shaft—
Fit—

Reading the result

A tolerance class such as H7 has a letter, which places the tolerance zone against the nominal size (the fundamental deviation), and a number, which sets the zone's width (the IT grade). Capitals are for holes, small letters for shafts. An H hole always has a lower deviation of zero, so it is the usual base of a fit (the hole-basis system); the shaft is then chosen for the fit wanted.

max clearance=largest hole−smallest shaftmin clearance=smallest hole−largest shaft\text{max clearance} = \text{largest hole} - \text{smallest shaft} \qquad \text{min clearance} = \text{smallest hole} - \text{largest shaft}
  • Clearance fit: the minimum clearance is not negative, so the hole is always larger than the shaft.
  • Interference fit: the maximum clearance is not positive, so the shaft is always larger than the hole. A negative clearance is interference.
  • Transition fit: the pair may have clearance or interference, depending on the actual sizes of the two parts.

The values on this page are calculated from the IT grade and fundamental deviation tables of ISO 286-1, for sizes up to 500 mm and the commonly used tolerance classes.