What is ISO 2768? ISO 2768 is an international standard created for general tolerances . It applies to linear dimensions, angular dimensions, radii, chamfers, and flatness/straightness that are not individually tolerance-indicated on a technical drawing.
| Nominal Size Range (mm) | Tolerance (mm) | | :--- | :--- | | 0.5 up to 3 | ±0.1 | | >3 up to 6 | ±0.1 | | >6 up to 30 | ±0.2 | | >30 up to 120 | ±0.3 | | >120 up to 400 | ±0.5 | | >400 up to 1000 | ±0.8 | | >1000 up to 2000 | ±1.2 | iso 2768-mk pdf
| Nominal Size Range (mm) | Tolerance (mm) | | :--- | :--- | | 0.5 up to 3 | ±0.2 | | >3 up to 6 | ±0.5 | | >6 up to 30 | ±1.0 | | >30 up to 120 | ±2.0 | Class k (sometimes called "K" or standard precision for geometry) applies to features that are not individually toleranced. Values are based on the nominal length of the feature . What is ISO 2768
| Nominal Length of Shorter Side (mm) | Tolerance (degrees/minutes) | | :--- | :--- | | 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' | | Nominal Size Range (mm) | Tolerance (mm)
| Part of Standard | Symbol | Meaning | Applies To | | :--- | :--- | :--- | :--- | | | m | Medium class | Linear dimensions (lengths, widths, depths) Angular dimensions Radii & chamfers | | ISO 2768-2 | k | K class (general tolerance for geometric features) | Straightness, flatness, perpendicularity, symmetry, runout | Common Confusion: Many engineers mistakenly think "mk" refers only to a machining finish. In reality, m governs size, while k governs shape and position. ISO 2768-1: Tolerances for Linear & Angular Dimensions (Class "m") When a drawing specifies class m (medium) , the following permissible deviations apply:
If you see a drawing note stating "General tolerances ISO 2768-mk" , the manufacturer must follow specific tolerance classes without cluttering the drawing with individual ± values for every hole, slot, or edge. The notation ISO 2768-mk combines two distinct tolerance classes from two parts of the standard:
| Tolerance Class | Straightness & Flatness (mm per 100mm) | Perpendicularity (mm per 100mm) | Symmetry (mm per 100mm) | | :--- | :--- | :--- | :--- | | | 0.2 | 0.3 | 0.5 |