How extrusion tolerances are defined
Industry standards (such as EN 755 in Europe and ANSI H35.2 in North America) define tolerance classes for extruded profiles — covering dimensions like wall thickness, angles, flatness, twist and length. The achievable precision depends on alloy, profile size and shape, and the specific dimension involved.
- Standard classes cover most commercial requirements
- Tighter precision is possible on selected features at added cost
- Wall thickness tolerance relates to the wall's size and position
- Straightness and twist degrade with length and profile complexity
What drives precision
Press capacity relative to the profile, die condition, alloy behavior, stretch and aging practices and the length of the piece all affect the tolerances actually held in production. Long structural pieces behave differently from short machined components.
Specifying tolerances smartly
Identify the features that are critical to fit or function and tolerance those deliberately. Leave everything else at standard classes — paying for precision that does nothing is one of the most common ways extrusion projects overspend.
- Mark critical-to-quality features on the drawing
- Tolerance fit-critical dimensions in the finished state (after coating)
- Confirm capability with the supplier before locking the drawing
- Agree inspection criteria for critical features
Fabrication and tolerance stacks
Cutting, drilling and machining add their own accuracy to the extrusion tolerance. For fabricated parts, review the whole stack — the base profile plus secondary operations — rather than tolerancing each operation in isolation.