ISO 2768 / GB/T 1804
ISO 2768 general tolerances by nominal size and class — choose the right tolerance class before you write a size tolerance on the drawing.
ISO 2768 / GB/T 1804 · Check the drawing edition · unit: mm
Values follow the ISO 2768-1 general tolerances for linear dimensions. GB/T 1804 uses the same class structure with different boundaries, so keep the two systems apart on the drawing.
| Nominal size range (mm) | Fine | Medium | Coarse | Very coarse |
|---|---|---|---|---|
| 0.5 to 3 | ±0.05 | ±0.1 | ±0.3 | ±0.5 |
| over 3 to 6 | ±0.05 | ±0.1 | ±0.3 | ±0.5 |
| over 6 to 30 | ±0.1 | ±0.2 | ±0.5 | ±1 |
| over 30 to 120 | ±0.15 | ±0.3 | ±0.5 | ±1.5 |
| over 120 to 400 | ±0.2 | ±0.5 | ±0.8 | ±2 |
| over 400 to 1000 | ±0.3 | ±0.8 | ±1.2 | ±2.5 |
| over 1000 to 2000 | ±0.5 | ±1.2 | ±2 | ±3 |
| over 2000 to 4000 | ±2 | ±3 | ±4 |
General tolerances never replace a size tolerance on a mating feature, and they say nothing about form, flatness or position. Pick the class the function of the part can live with, then tighten only the features that matter. The classes and the size ranges below follow ISO 2768-1; GB/T 1804 uses the same idea but its own class boundaries, so keep the two systems apart on the drawing.
Reference source
ISO 2768 / GB/T 1804
ISO 2768 is a general geometrical tolerance standard for untoleranced linear and angular dimensions. It lets you put a single note on the drawing instead of tolerancing every dimension separately. It is suitable for machined or fabricated parts where the function does not depend on a tight individual tolerance, for example covers, brackets and housings.
Medium is the usual default for general engineering parts. Fine suits smaller, more accurate assemblies where the feature size is under about 30 mm. Coarse and very coarse suit large weldments and structures where the tolerance is dominated by fabrication and coating. Choose the coarsest grade your assembly can still live with, because each step costs money.
No. ISO 2768 covers untoleranced linear and angular dimensions only. Hole diameters, thread sizes, radii and chamfers, and every dimension that carries a specific fit need their own callout. A general tolerance note never replaces a size tolerance on a mating feature.
They follow the same principle and the same class structure, but the class boundaries and the value tables are not identical. GB/T 1804 is the Chinese national standard and is still widely used on drawings issued in China. If the drawing must be read in both regions, state the standard explicitly instead of relying on an assumed equivalence.
Yes, and that is the normal practice. The general tolerance note covers every dimension that has no individual tolerance. Individual callouts always win over the general note, so you can tighten the few functional features and leave the rest to the general class.
The tolerance for that single dimension is agreed between the customer and the manufacturer and entered on the drawing. Large weldments and castings usually end up in this situation, so agree the values before production starts rather than during the first inspection report.
No. ISO 2768 is a dimensional tolerance standard. Form and orientation characteristics are controlled separately, either with a general geometrical tolerance such as ISO 2768-2 or with individual geometric tolerancing callouts on the drawing.
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