On every technical drawing there is a line like "ISO 2768-mK". Most people copy it without knowing what it means. Here is the simple explanation.
What is ISO 2768?
ISO 2768 is the standard for general tolerances — the tolerances that apply to every dimension on a drawing that does not carry its own specific tolerance. Instead of writing a tolerance next to each dimension, you state one class once, in the title block, and it covers everything else.
ISO 2768 is what lets a drawing stay readable: one line in the title block instead of a tolerance on every single dimension.
The two parts: linear and geometric
ISO 2768 has two independent parts, and that is why you see two letters.
- Part 1 covers linear and angular dimensions. Its classes are f (fine), m (medium), c (coarse), v (very coarse).
- Part 2 covers geometric tolerances (flatness, perpendicularity, symmetry). Its classes are H, K, L.
So "ISO 2768-mK" means: medium class for dimensions, K class for geometry. "ISO 2768-fH" means fine dimensions, H geometry — a tighter overall specification.
What the classes mean in practice
| Dimension (e.g. 30 to 120 mm) | Class f | Class m | Class c |
|---|---|---|---|
| Tolerance | ±0.15 mm | ±0.3 mm | ±0.8 mm |
The tolerance widens with the size of the dimension: a large dimension gets a wider tolerance than a small one, within the same class.
Which class to choose
For standard bent sheet metal, ISO 2768-mK is the right choice in the vast majority of cases. It is the realistic class for laser cutting and press brake bending.
Choosing class f "to be safe" is a costly mistake. It forces inspections and reworks for a precision that bent sheet metal cannot reliably deliver anyway.
Reserve tight tolerances for the few specific dimensions that genuinely need them — and write those directly next to the dimension, not as a general class.
DRAWLESS applies ISO 2768 automatically
Every drawing generated by DRAWLESS carries an ISO 2768-mK title block by default, with correctly placed dimensions and tolerances. You get a normalized, professional drawing without filling in a title block by hand — and you can specify tighter tolerances on individual dimensions when a part truly requires it.