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is an international standard used to define "general tolerances" for manufacturing. By adding this single note to a technical drawing's title block, an engineer sets a default permissible variation for every dimension that doesn't have an explicit tolerance.
Implementing this standard on technical drawings provides several distinct advantages for engineering teams and machinists:
The notation "mK" combines two distinct parts of the standard:
| Nominal Length of Shorter Side (mm) | Permissible Deviation (mm/m or degrees) | | :--- | :--- | | Up to 10 | ±1° | | >10 up to 50 | ±0°30' | | >50 up to 120 | ±0°20' | | >120 up to 400 | ±0°10' | | >400 | ±0°5' | general tolerance iso 2768-mk
Symmetry limits apply to parallel features or slots that share a central datum plane. Nominal Length Range (mm) Symmetry Tolerance (mm) for Class "k" Over 100 to 300 Over 300 to 1000 Over 1000 to 3000 4. Run-Out (Circular Run-Out)
Angular tolerances apply to the length of the shorter leg of the angle.
A factory in Germany (where it is often called DIN ISO 2768 ) and a factory in China understand the exact same limits. is an international standard used to define "general
Understanding where 'mk' fits in the hierarchy helps designers choose correctly.
Machinists know exactly which features require precision setups and which features can be run quickly using standard shop capabilities. Over-tolerancing is a primary driver of unnecessary manufacturing costs.
While ISO 2768-mK is an exceptional baseline, it should not be applied blindly. Engineers must override the general tolerance in the following situations: Nominal Length Range (mm) Symmetry Tolerance (mm) for
ISO 2768 was built primarily for metal removal (machining) and sheet metal fabrication. For highly flexible plastics, rubbers, or complex 3D-printed parts, standard machining tolerances may be unachievable or irrelevant.
Always remember the golden rule of drafting: