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 skimping but a range permitted by the standard — however, **you must state at 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 practice, orders may also use "restricted negative tolerance" (e.g. 1.5 mm guaranteed ≥1.45), usually at a price premium of 1–3%, but it ensures the finished thickness after cutting.
When tolerances must be tightly controlled
- Pressure and structural calculations: wall thickness is a design input, and negative tolerance directly reduces load-bearing capacity. Such orders should state "acceptance by minimum thickness".
- Deep-drawn parts: thickness variation changes the stress distribution during drawing, raising the cracking rate.
- Continuous stamping from coil: thickness variation within a coil matters more than in a single sheet; you can require a thickness range within the same coil of ≤ 0.03 mm.
- Orders priced by weight: negative tolerance means the actual delivered weight is lower; for long-term purchasing, write the tolerance into the contract to avoid disputes.
How to specify it 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 how out-of-tolerance material is handled (return / downgrade with price reduction). Writing only "1.5 mm" is where disputes begin.
