In mechanical engineering, specifying individual tolerances for every single dimension on a technical drawing is highly inefficient. It clutters blueprints, increases design time, and raises manufacturing costs.
When manufacturing a mechanical part, achieving absolute perfection in dimensions is physically impossible. Minor variations always occur due to tool wear, machine vibrations, and material expansion. To ensure parts fit together without requiring expensive, hyper-precise measurements for every single dimension, engineers use general tolerances.
These control the angular variations of intersecting lines or surfaces, measured in degrees and minutes. Length of Short Side ( Tolerance Limit for Class "m" ±1∘plus or minus 1 raised to the composed with power ISO 2768 Part 2: Geometrical Tolerances (Class "K") general tolerance iso 2768-mk
General tolerances for circularity and total run-out are often handled by the same principles as the straightness/flatness of the related surfaces. KEYENCE CORPORATION OF AMERICA Application & Implementation Drawing Note:
O-ring grooves and sealing surfaces require incredibly tight control over depth and surface finish to prevent leaks. Minor variations always occur due to tool wear,
| Nominal Length Range (mm) | Permissible Deviation ('K' Class, mm) | | :--- | :--- | | up to 10 | 0.05 | | over 10 up to 30 | 0.10 | | over 30 up to 100 | 0.20 | | over 100 up to 300 | 0.40 | | over 300 up to 1000 | 0.60 | | over 1000 up to 3000 | 0.80 |
Linear tolerances scale with the size of the dimension. Larger features are allowed more variation than smaller features because they are harder to measure and control during manufacturing. Length of Short Side ( Tolerance Limit for
These tolerances apply to internal sizes, external sizes, steps, diameters, and radii. Nominal Size Range (mm) Tolerance Limits for Class m (mm) 120 to 400 400 to 1000 1000 to 2000 2000 to 4000 2. Broken Edges (External Radii and Chamfer Heights)
If your assembly has a critical mating part—such as a bearing press-fit or a sealed O-ring groove—the general tolerances of ISO 2768-mk will likely be too loose. In these scenarios, you must (e.g., or a fit callout like