Imagine designing a gearbox. The gears inside require "Fine" tolerances, but the outer cast housing only needs "Coarse" tolerances. ISO 20457 provides a systematic way to assign these levels without over-specifying (which increases cost) or under-specifying (which causes assembly failure).
The standard provides tolerance tables categorized by the and the Material Group . iso 20457 tolerance table pdf
: Materials are categorized (typically Categories 1–4) based on their shrinkage properties. Precision Classes Class A (High Precision) Imagine designing a gearbox
Standard measurement temperature (usually 23°C) and humidity (50% RH). iso 20457 tolerance table pdf