The actual thickness of stainless steel sheet is generally thinner than the nominal value (negative tolerance rolling, an industry convention). So "1.5 mm" under different standards and different tolerance grades may measure 1.35–1.62 mm. This is not material shorting, but the range permitted by the standard — however, **you must state clearly at the time of ordering which grade will be used for acceptance**.
Two commonly used systems
| Standard | Width | Permissible deviation for 1.5 mm nominal (common grades) |
|---|---|---|
| ASTM A480 (cold-rolled) | ≤ 1250 mm | ± 0.08 mm (tighter grade) |
| EN 10088-2 (cold-rolled) | ≤ 1250 mm | ± 0.09 mm (standard grade) |
| GB/T 3280 (cold-rolled) | ≤ 1250 mm | ± 0.10 mm (standard grade) |
In actual ordering there is also the practice of "limited negative tolerance" (e.g., 1.5 mm guaranteed ≥1.45), with prices usually 1–3% higher, but it ensures the finished thickness after cutting.
When tolerances must be strictly controlled
- Pressure-bearing and structural calculations: Wall thickness is a design input, and negative tolerance directly reduces load-bearing capacity. Such orders must state "acceptance by minimum thickness".
- Deep-drawn parts: Thickness variation changes the stress distribution during drawing, leading to a higher cracking rate.
- Continuous stamping of coils: Thickness variation within a coil is more critical than in single sheets; you can require the thickness range within the same coil to be ≤ 0.03 mm.
- Orders priced by weight: Negative tolerance means the actual delivered weight is lower; for long-term procurement, tolerances should be written into the contract to avoid disputes.
How to specify to avoid disputes: Write in the contract "thickness to be judged per ASTM A480, measurement points ≥25 mm from the edge, three points per sheet", and agree on the handling of out-of-tolerance (return / downgrade with price reduction). Writing only "1.5 mm" is the starting point of disputes.
