ANSI H35.2 Aluminum Tolerances Explained
ANSI H35.2 aluminum tolerances explained — extrusion, sheet, plate, and tube limits, how to read the tables, and how to call out the standard.
Introduction
Aluminum is one of the most forgiving metals to fabricate, but no mill, extruder, or fabricator produces a perfectly dimensioned part every time. Buyers who assume “aluminum is aluminum” soon discover parts that will not assemble. ANSI H35.2 exists to remove that guesswork: it is the Aluminum Association's standard for dimensional tolerances on aluminum mill products.
This guide explains what ANSI H35.2 covers, how its tolerance tables are structured, how it compares with ASTM and ISO/EN standards, and how to call it out on a drawing so that every quote and inspection uses the same numbers.
Start with an overview of our [CNC machining capabilities](/en/solutions/cnc-machining) to see how tolerances are held in production.
What Is ANSI H35.2?
ANSI H35.2 — formally “Dimensional Tolerances for Aluminum Mill Products” — is published by the Aluminum Association and approved as an American National Standard. It collects, in one reference, the permissible dimensional variation for the full range of wrought aluminum products: extruded profiles, rolled sheet and plate, drawn tube, rod, bar, and wire.
Before H35.2, each producer published its own tolerance tables, so a “3.2 mm” wall meant different things at different mills. ANSI H35.2 harmonized those tables into a single industry baseline that buyers, engineers, and inspectors can cite by name.
The standard exists in two parallel editions: the customary (inch) version, ANSI H35.2, and the metric version, ANSI H35.2M. Always state which system your drawing uses, because the two versions round differently.
Products and Tolerances Covered
ANSI H35.2 organizes tolerances by product form, because the manufacturing route — extrusion, rolling, or drawing — determines which dimensions are hard to hold.
**Extruded profiles.** Extrusion tolerance is the most-cited section of H35.2. Dimensions are grouped by cross-sectional thickness and by the profile's circumscribing circle diameter (CCD), the smallest circle that encloses the cross-section. As wall thickness and CCD grow, the allowed deviation increases. Typical tables cover wall thickness, cross-sectional dimensions, straightness, twist, flatness, and length.
**Sheet, plate, and coiled sheet.** For flat rolled products the standard covers thickness, width, length, camber, squareness, and flatness. Thickness tolerance widens with nominal gauge and with width, and tight “precision” thickness bands are available on request.
**Drawn tube, rod, and bar.** For tube and bar, H35.2 specifies outside diameter, inside diameter, wall thickness, straightness, length, and squareness of cut ends — the numbers fabricators rely on when parts are fed automatically into a machine.
Key Tolerance Categories
Across product forms, the same families of tolerance recur:
How to Read the Tolerance Tables
Every H35.2 table is a matrix: find your nominal dimension along one axis and the governing process or geometry (thickness, CCD, or width) along the other, then read the permitted plus/minus value at the intersection.
Two habits prevent mistakes. First, note whether a value is a total spread or a ± figure; the tables use both. Second, remember that tolerances are additive in assembly — a wall thickness on the high side plus a hole on the low side can still miss a fit, even though each part is individually acceptable.
For a deeper look at how tolerance stacks are managed in metal components, see our [CNC machining tolerances guide](/en/blog/cnc-machining-tolerances-guide).
ANSI H35.2 vs Other Standards
ANSI H35.2 is the aluminum-specific baseline, but it is rarely used alone:
Because the permitted values differ between systems, never mix a callout from one standard with inspection to another. State the standard, edition, and product form explicitly.
For alloy selection to go with your tolerance callouts, see our [metal material selection guide](/en/blog/metal-material-selection-guide).
Calling Out ANSI H35.2 on a Drawing
Designers who apply tolerances only where the function requires them cut cost without sacrificing fit. Our [stamping service page](/en/solutions/stamping) shows the same principle applied to formed sheet parts.
Inspection and Quality Control
Tolerances are only meaningful if they are measured. Reliable suppliers verify H35.2 dimensions with calibrated instruments — micrometers and calipers for thickness and wall, dial indicators and height gauges for straightness and flatness, and CMMs or optical comparators for complex extruded profiles. First-article inspection reports, material certificates, and dimensional reports should accompany production lots, and critical dimensions should be part of an ongoing SPC program. Ask for the measurement method, because a buyer who inspects with different equipment than the mill may read a different result.
FAQ
Is ANSI H35.2 mandatory?
It is a voluntary consensus standard, but it becomes contractual the moment a purchase order or drawing references it. Many aluminum suppliers and OEMs treat it as the default.
Does ANSI H35.2 apply to machined or stamped parts?
No — it governs mill products. Once a profile is machined, stamped, or welded, the finished-part tolerances are set by the drawing and by machining standards such as ISO 2768.
What is CCD and why does it matter?
The circumscribing circle diameter is the smallest circle that contains an extrusion's cross-section. H35.2 uses CCD, together with wall thickness, to select the right tolerance row, so larger, more complex profiles are allowed more variation.
Conclusion
ANSI H35.2 turns “how close is close enough?” into a documented, quotable answer for aluminum extrusions, sheet, plate, rod, bar, and tube. Cite the standard and edition on every drawing, apply tight tolerances only where the function demands them, and confirm that your supplier inspects to the same system — then aluminum parts assemble the first time.
MetalBizz machines, stamps, and finishes aluminum parts with full dimensional inspection and DFM feedback. Upload your CAD files for a free quotation within 24 hours.