This standard simplifies drawings by providing a set of rules for general tolerances. When a drawing references , it applies standard accuracy limits to all dimensions that do not have explicitly stated tolerances.
These values limit how much a surface or edge can bow or warp over its total length: Nominal Length Range (mm) Tolerance Limit (mm) 100 to 300 300 to 1000 1000 to 3000 Perpendicularity
When a drawing specifies ISO 2768-mK, it also invokes the class for geometrical tolerances. These control the form and position of features without individual callouts.
General tolerances for geometric characteristics (straightness, flatness, symmetry, etc.). Decoding "mK" Tolerance Iso 2768 Mk Pdf
| Tolerance Class | Up to 10 mm | >10 to 30 mm | >30 to 100 mm | >100 to 300 mm | >300 to 1000 mm | >1000 to 3000 mm | | :--- | :--- | :--- | :--- | :--- | :--- | :--- | | | 0.02 mm | 0.05 mm | 0.1 mm | 0.2 mm | 0.3 mm | 0.4 mm | | K | 0.05 mm | 0.1 mm | 0.2 mm | 0.4 mm | 0.6 mm | 0.8 mm | | L | 0.1 mm | 0.2 mm | 0.4 mm | 0.8 mm | 1.2 mm | 1.6 mm |
It is important to note that ISO 2768 is not a universal standard. It is most common in Europe and Asia. In the United States, the dominant standard for general tolerances is often implied by the number of decimal places on a dimension per ASME Y14.5.
| Class | Description | Typical Use | |-------|-------------|--------------| | | High precision | Instruments, small mechanisms | | m (Medium) | General machining | Brackets, housings, structural parts | | c (Coarse) | Fabrication | Welded frames, sheet metal, casting | | v (Very coarse) | Rough cuts | Forging, sand casting, clearance-only | This standard simplifies drawings by providing a set
While you can use it, molded parts warp. Class "c" (Coarse) is often better for plastics. Class mK is ideal for metal after machining.
| Nominal Dimension Range | Tolerance for "m" (Medium) | | :--- | :--- | | 0.5 mm up to 3 mm | ± 0.1 mm | | > 3 mm up to 6 mm | ± 0.1 mm | | > 6 mm up to 30 mm | ± 0.2 mm | | > 30 mm up to 120 mm | ± 0.3 mm | | > 120 mm up to 400 mm | ± 0.5 mm | | > 400 mm up to 1000 mm | ± 0.8 mm | | > 1000 mm up to 2000 mm | ± 1.2 mm |
Quality assurance (QA) teams can use standard lookup tables to inspect non-critical dimensions, speeding up verification and reducing production bottlenecks. These control the form and position of features
Refers to ISO 2768-2 , representing the "K" tolerance class for general geometrical tolerances (e.g., flatness, straightness, and symmetry). ISO 2768-1: Linear & Angular Dimensions (Class "m")
For broken edges, external radii, and chamfer heights, the permissible deviations for the m class are: