What is ISO 2768?
ISO 2768 defines general tolerances for linear and angular dimensions that have no individual tolerance on the drawing. It has two parts:
- ISO 2768-1: tolerances on linear and angular dimensions (classes f, m, c, v)
- ISO 2768-2: tolerances on form and positional features (classes H, K, L)
Example title block entry: ISO 2768-mK means linear class "m" (medium) and geometric class "K".
The 4 ISO 2768-1 tolerance classes
| Class | Name | Example (30 mm dimension) |
|---|---|---|
| f | Fine | ± 0.05 mm |
| m | Medium | ± 0.1 mm |
| c | Coarse | ± 0.2 mm |
| v | Very coarse | ± 0.5 mm |
Should ISO 2768 general tolerances be ballooned?
Yes, absolutely. Omitting general title block tolerances is one of the most common ballooning errors. EN9102 / AS9102 is explicit: all drawing characteristics must be ballooned, including general tolerances. Two approaches are common:
- Method 1 — Single balloon: one balloon references "
ISO 2768-mK" as a global characteristic in Form 3 - Method 2 — Individual balloons: each untoleranced dimension gets a balloon, with its tolerance extracted from the ISO 2768 table by nominal value
Method 2 is more complete but generates a larger Form 3. Method 1 is acceptable for many customers if the general tolerance is clearly referenced.
BullePlan and ISO 2768: automatic extraction
During AI analysis, BullePlan detects general tolerance references in the title block (ISO 2768, ASME title block…) and automatically includes them in the generated Form 3 table, ensuring a complete and compliant output.