| Nominal Length of Shorter Side (mm) | Tolerance (mm per meter) | Tolerance (degrees/minutes) | | --- | --- | --- | | Up to 10 | ±1° | ±1° | | >10 to 50 | ±0°30' | ±0°30' | | >50 to 120 | ±0°20' | ±0°20' | | >120 to 400 | ±0°10' | ±0°10' | | >400 | ±0°5' | ±0°5' | This is where ISO 2768-mk becomes stricter than the 'f' (fine) class. Class 'k' tolerances are tighter than 'L' (coarse) but looser than 'H' (precision). The values depend on the nominal length of the feature.
If a shaft length is specified as 50 mm with no individual tolerance, ISO 2768-mk permits a length between 49.7 mm and 50.3 mm. Radii and Chamfers (Class 'm') | Nominal Dimension Range (mm) | Tolerance (mm) | | --- | --- | | 0.5 to 3 | ±0.2 | | >3 to 6 | ±0.5 | | >6 to 30 | ±1.0 | Angular Dimensions (Class 'm') Angular tolerances are not constant; they depend on the length of the shorter side of the angle. general tolerance iso 2768-mk
A 200 mm long milled surface under ISO 2768-mk must not warp by more than 0.2 mm (flatness). Its end face must be perpendicular to its base within 0.4 mm over the full length. ISO 2768-mk vs. Other Tolerance Classes Understanding where 'mk' fits in the hierarchy helps designers choose correctly. | Nominal Length of Shorter Side (mm) |
Use ISO 2768-mk for the majority of machined, cast, or 3D-printed metal parts where features assemble without extreme precision. Save specific tolerances only for critical interfaces. This practice will elevate your engineering drawings from ambiguous sketches to professional, internationally compliant manufacturing instructions. If a shaft length is specified as 50
For the designer, using 'mk' cleans up drawings and signals a mature understanding of manufacturing realities. For the machinist, it provides clear, enforceable limits for size and geometry. For the quality engineer, it defines the precise inspection criteria.