General Tolerances for Linear Dimensions
General tolerances for linear dimensions are defined in the standard ISO 2768-1:1989. These tolerances apply to all linear measurements – such as lengths, widths, heights, diameters, and radii – whenever specific tolerances are not indicated on the drawing. This makes drawings clearer and ensures more consistent manufacturing.
The standard divides tolerances into four accuracy classes: f (fine), m (medium), c (coarse), and v (very coarse). The choice of class depends on how precise the measurement needs to be. Smaller dimensions allow for very tight deviations, while larger dimensions permit wider variation. This helps keep manufacturing both practical and cost-effective.
For example, a drawing marked with ISO 2768-m means that all length measurements follow the medium accuracy class, unless a particular measurement is specified with a different tolerance.
General Tolerance Table for Linear Dimensions
| Tolerance Class | Permitted Deviations by Nominal Dimension Range | |||||||||
| Symbol | Description | > | 0.5 | 3 | 6 | 30 | 120 | 400 | 1000 | 2000 |
| ≤ | 3 | 6 | 30 | 120 | 400 | 1000 | 2000 | 4000 | ||
| f | fine | 0.05 | 0.05 | 0.1 | 0.15 | 0.2 | 0.3 | 0.5 | - | |
| m | medium | 0.1 | 0.1 | 0.2 | 0.3 | 0.5 | 0.8 | 1.2 | 2 | |
| c | coarse | 0.2 | 0.3 | 0.5 | 0.8 | 1.2 | 2 | 3 | 4 | |
| v | very coarse | - | 0.5 | 1 | 1.5 | 2.5 | 4 | 6 | 8 | |
The values in the table are given in millimeters (mm)
