General Tolerance Iso 2768-mk -
This report is designed as a practical guide for engineers, drafters, and quality control inspectors to understand, apply, and inspect tolerances based on this standard.
For Machinists & Quality Control
- Measurement Uncertainty: When inspecting a part marked
ISO 2768-mK, a measurement of 25.15 mm on a 25 mm nominal length is Acceptable (Tolerance is ±0.2 for range 6-30mm). A measurement of 25.25 mm is Rejectable. - Cost Efficiency: This standard prevents "over-inspection." Inspectors do not need to verify every dimension to the micrometer unless specified; they verify it against the "m" or "K" tables.
- Geometry Checks: A "K" class part does not just need to fit dimensionally; it must also pass flatness and perpendicularity checks. For example, a surface 150mm long must not bow more than 0.4mm (Flatness).
4.1 Key Geometrical Tolerances for Class K
| Geometrical Character | Nominal Size Range (mm) | Tolerance (mm) | | :--- | :--- | :--- | | Straightness & Flatness | Up to 10 | 0.05 | | | Over 10 up to 30 | 0.1 | | | Over 30 up to 100 | 0.2 | | | Over 100 up to 300 | 0.4 | | | Over 300 up to 1000 | 0.6 | | Perpendicularity | Up to 100 | 0.4 | | | Over 100 up to 300 | 0.6 | | | Over 300 up to 1000 | 0.8 | | Symmetry | Up to 100 | 0.6 | | | Over 100 up to 300 | 0.8 | | | Over 300 up to 1000 | 1.0 | | Run-out (Circular) | Any length | 0.3 | general tolerance iso 2768-mk
Note: According to ISO 2768-2, general tolerances for cylindricity are not specified; the tolerance is deemed to be equal to the tolerance for circularity (run-out). This report is designed as a practical guide
For Designers
- Drawing Indication: You must write
ISO 2768-mKin the title block or near the drawing number. - Exceptions: If a specific dimension requires tighter or looser tolerance than the general standard, you must specify it explicitly (e.g.,
25.00 -0.05/+0.00). Explicit tolerances always override general tolerances. - Sanity Check: Ensure your design functions correctly with these tolerances. Class "m" assumes standard machining or good quality 3D printing.