When specifying sheet metal components, tolerance selection is one of the most critical decisions a procurement engineer makes. Too loose and your assembly won't fit. Too tight and you pay 3× the cost for capability you don't need.
This guide explains the ISO 2768-m standard — the most common default tolerance class for sheet metal fabrication — and when to deviate from it.
What is ISO 2768?
ISO 2768 defines general tolerances for linear and angular dimensions without individual tolerance indications. It has two parts: Part 1 covers linear and angular dimensions; Part 2 covers geometric tolerances.
The four tolerance classes are: f (fine), m (medium), c (coarse), and v (very coarse). For sheet metal, ISO 2768-m (medium) is the standard default.
ISO 2768-m Linear Tolerances
| Dimension Range | Tolerance (±mm) |
|---|---|
| 0.5 – 3mm | ±0.1 |
| 3 – 30mm | ±0.2 |
| 30 – 120mm | ±0.3 |
| 120 – 400mm | ±0.5 |
| 400 – 1000mm | ±0.8 |
| 1000 – 2000mm | ±1.2 |
Bend Angle Tolerances (ISO 2768-m)
For bent sheet metal: up to 10mm arm length = ±1°. 10–50mm = ±0.5°. Above 50mm = ±0.3°.
When to Specify Tighter
Tighter tolerances are needed when: parts mate directly without adjustment, PCB mounting holes require precise pitch, enclosure doors must seal against gaskets. Always mark critical dimensions explicitly in your drawing.
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