Basic size, tolerance zone and fit
Basic size is the design starting point; upper and lower deviations define the permitted range; the tolerance zone describes its width and position; fit describes the relationship between shaft and hole. “h6” without a basic size, mating hole or function is incomplete.
ISO 286-1 provides the code system for cylindrical linear sizes and explains basic-hole and basic-shaft principles, but it does not choose the fit for the designer.
One size tolerance cannot replace geometry
A conforming diameter does not prove that a shaft is straight. Size, straightness, roundness, cylindricity and run-out are different characteristics and should be specified according to function.
For long shafts, define effective length, excluded ends, support and rotational or static measurement method.
Agree the measurement definition
ISO 14405-1:2025 provides tools for specifying linear-size characteristics. A purchase order need not reproduce the standard, but it should avoid ambiguous phrases such as “measure anywhere.”
ISO 1:2022 establishes the reference-temperature concept for dimensional and geometrical properties. Precision or long-length acceptance may require temperature equilibrium, instrument capability, locations and decision rules.
Recommended order wording
Put basic size + limit deviations/tolerance code + effective length + critical geometry + measurement conditions + mating component into the same traceable document. Define units and endpoints for any company-specific negative-tolerance range.