The second letter refers to (Geometric tolerances). The classes are H, K, L .
If you need a precision shaft to slide into a hole, you must use a standard like ISO 286 (e.g., H7/g6) instead of general tolerances.
Perpendicularity requires a datum feature. The tolerance depends on the length of the shorter leg forming the 90∘90 raised to the composed with power Nominal Length Range ( Tolerance Limit for Class "K" ( 3. Symmetry
depending on scale) for general linear, angular, and geometrical tolerances. It ensures parts fit together reliably without forcing manufacturers into unnecessary, costly over-precision.
ISO 2768-1 features four tolerance classes: fine (f), medium (m), coarse (c), and very coarse (v). The "m" class balances manufacturing feasibility with functional precision.
Simplified angular tolerance:
Aerospace or automotive engine components often require strict geometric limits (Class H or custom GD&T) to prevent mechanical failure. ✅ Summary of ISO 2768-mK
Parts made from plastics or materials with high thermal expansion (the standard is primarily designed for metal removal/machining). Dimensions where safety or critical function is at stake.