What is ISO 2768?
ISO 2768 is an international standard that defines general tolerances for linear and angular dimensions that do not have individually specified tolerances on technical drawings. The standard consists of two parts:
- ISO 2768-1: Tolerances for linear and angular dimensions
- ISO 2768-2: Geometrical tolerances
ISO 2768-1 Tolerance Classes
The standard defines four accuracy classes: fine (f), medium (m), coarse (c), very coarse (v).
Linear Dimensions Tolerance Table [mm]
| Dimension Range [mm] | f (fine) | m (medium) ⭐ | c (coarse) | v (very coarse) |
|---|---|---|---|---|
| 0.5 - 3 | ±0.05 | ±0.1 | ±0.2 | - |
| 3 - 6 | ±0.05 | ±0.1 | ±0.3 | ±0.5 |
| 6 - 30 | ±0.1 | ±0.2 | ±0.5 | ±1.0 |
| 30 - 120 | ±0.15 | ±0.3 | ±0.8 | ±1.5 |
| 120 - 400 | ±0.2 | ±0.5 | ±1.2 | ±2.5 |
| 400 - 1000 | ±0.3 | ±0.8 | ±2.0 | ±4.0 |
| 1000 - 2000 | ±0.5 | ±1.2 | ±3.0 | ±6.0 |
Angular Dimensions Tolerance Table
| Short Side Range [mm] | f (fine) | m (medium) ⭐ | c (coarse) | v (very coarse) |
|---|---|---|---|---|
| up to 10 | ±1° | ±1° | ±1°30' | ±3° |
| 10 - 50 | ±30' | ±30' | ±1° | ±2° |
| 50 - 120 | ±20' | ±20' | ±30' | ±1° |
| 120 - 400 | ±10' | ±10' | ±15' | ±30' |
| above 400 | ±5' | ±5' | ±10' | ±15' |
Why ISO 2768-Medium is the Standard
The ISO 2768-m (medium) class is the most commonly used because:
- It matches the capabilities of standard CNC machines
- Provides sufficient accuracy for 90% of industrial applications
- Cost-effective – does not require additional finishing operations
- Accepted by most industries: automotive, machinery, electronics
- Supported by most CAD/CAM systems as the default value
How to Indicate ISO 2768 on Drawings
On the title block of a technical drawing, use the following notation:
- ISO 2768-m – medium class (most common)
- ISO 2768-f – fine class (precision parts)
- ISO 2768-c – coarse class (welded constructions)
- ISO 2768-mK – medium class with geometrical tolerances K
Application in Sheet Metal Processing
For sheet metal elements manufactured by:
- Laser cutting: dimensional tolerances achieve ISO 2768-c to ISO 2768-m
- Punching: ISO 2768-m possible with well-maintained dies
- CNC bending: bending angles conform to ISO 2768-m on calibrated press brakes
- Milling holes: ISO 2768-f achievable for post-cut holes
Practical Examples
Example 1 – Linear dimension: 100mm with ISO 2768-m tolerance:
Actual dimension may be 100mm ±0.3mm, i.e., 99.7 – 100.3mm
Example 2 – Angle: 90° with ISO 2768-m tolerance (short side 80mm):
Actual angle may be 90° ±20 minutes, i.e., 89°40' – 90°20'