ASTM A480 Stainless Steel Plate Thickness Tolerances

What Is ASTM A480

ASTM A480 is the general requirements specification for stainless steel flat-rolled products, including plates, sheets, and strips. Among its many requirements, the thickness tolerance tables define the allowable variation in product thickness during manufacturing. Thickness tolerances directly affect fit-up, strength calculations, and final performance, so selecting the correct tolerance class is essential for smooth processing and assembly.

Why Thickness Tolerances Matter

Controlled thickness tolerances ensure dimensional accuracy, so machined parts and welded assemblies fit as designed and mechanical strength meets the expected standards. Strict control avoids processing difficulties caused by oversized or undersized material, reduces rework cost, and supports corrosion resistance and structural safety through uniform thickness. Specifying an appropriate tolerance also avoids paying for unnecessarily tight control.

Typical Tolerance Values

For common plate thicknesses the tolerances are approximately plus or minus 0.13 mm for thicknesses up to 6.35 mm, plus or minus 0.18 mm for 6.35 to 12.7 mm, plus or minus 0.25 mm for 12.7 to 25.4 mm, plus or minus 0.38 mm for 25.4 to 50.8 mm, and plus or minus 0.51 mm above 50.8 mm. Actual permitted deviations depend on plate width, product form, and finish, and are tabulated in the current edition of ASTM A480.

Reading the Tolerance Tables

The A480 tables give separate plus and minus allowances for each width and thickness band. For example, a 12.70 mm plate with a 1524 mm width may carry an allowance in the region of minus 0.25 mm and plus 1.37 mm, meaning any measured thickness between the minimum and maximum values complies. Always consult the exact table for the product width and thickness ordered.

Procurement Considerations

When purchasing stainless plates, specify the nominal thickness, width, and required tolerance class. Consider downstream processing: grinding, machining, or laser cutting removes material, so account for the minimum thickness when the finished part has a strict thickness requirement. Request the mill test report to confirm measured values.

Frequently Asked Questions

Q: What does ASTM A480 govern?

A: General requirements for stainless steel plate, sheet, and strip, including thickness tolerances.

Q: What is the tolerance for a 12.7 mm plate?

A: Approximately plus or minus 0.18 mm for standard widths, with width-dependent values in the tables.

Q: Why do tolerances matter?

A: They control fit, strength, corrosion performance, and procurement cost.

Q: Do tolerances depend on width?

A: Yes, both width and nominal thickness determine the allowed deviation.

Q: How do I verify compliance?

A: Measure at any point and compare with the applicable A480 table values.

Q: Should I specify tighter tolerances?

A: Only where downstream processing demands it, to control cost.

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