Aluminium profile tolerances: EN 755-9, EN 12020-2 and what they actually cover
Two different standards govern the tolerances of an extruded aluminium profile, and which one applies is not a matter of preference: it depends on the alloy, the size of the section and the shape of its walls. Both standards also cover more than dimensions. They set limits on form, which is where most rejected deliveries actually come from. This guide explains how to tell the two apart, what qualifies a profile for the tighter one, and how to check a delivery without a measuring room.
Two standards, not one
Extruded profiles are covered by two separate tolerance standards. They are not an older and a newer version of the same document. They describe two levels of precision for two different purposes.
| Aspect | EN 755-9 | EN 12020-2 |
|---|---|---|
| Intended for | Profiles for general engineering | Precision profiles, largely architectural |
| Alloys | No restriction to specific grades | EN AW-6060 and EN AW-6063 only |
| Circumscribing circle, maximum | 800 mm | 350 mm |
| Tolerances | Standard, graded by alloy group | Tighter |
| Visible surfaces | No special requirement | Stricter requirements on surface condition |
The practical consequence is easy to miss. Two profiles with the same catalogue dimensions can carry different guaranteed accuracy, because each was supplied to a different standard.
It shows up wherever the profile has to fit something: a section sliding into a groove, mating parts of a frame, an end cap seating flush. Where a profile is simply cut and bolted, it usually does not matter at all.
The four conditions for EN 12020-2
The tighter standard does not apply on request. A profile has to meet several conditions at once, and failing any one of them puts it back under EN 755-9.
| Condition | Limit |
|---|---|
| Alloy | EN AW-6060 or EN AW-6063 |
| Diameter of the circumscribing circle | 350 mm or less |
| Mass of the profile | 10 kg/m or less |
| Ratio of thickest to thinnest wall | 3.5 or less |
The last line is the one that surprises people, and it has a physical reason. A section that combines a heavy wall with a very thin one cools unevenly after extrusion, so it distorts. The standard excludes such sections from its tighter category rather than promising accuracy it cannot deliver.
Ordinary structural sections in 6060 and 6063 meet these conditions comfortably. For large or shape-heavy sections it is worth checking whether the tighter standard applies at all before quoting it in a specification. Alloy selection itself is covered in the guide to EN AW aluminium alloys.
Alloy groups change the tolerance within EN 755-9
EN 755-9 is often quoted as a single level of accuracy. It is not.
The standard sorts alloys into two groups according to how difficult they are to extrude, and the tolerance tables differ between them. Softer, easily extruded alloys sit in one group; the harder, higher-strength alloys sit in the other and are allowed wider limits.
This matters when a design moves from one alloy to another. Switching a section from a readily extruded grade to a higher-strength one does not only change the mechanical values. It can also widen the tolerance the supplier is obliged to hold, on the same drawing and the same nominal dimensions.
If a dimension is critical, name both the alloy and the tolerance standard on the order, and state which dimension is critical.
Tolerances cover form, not just dimensions
The full title of both standards ends with the words tolerances on dimensions and form. The second half of that pair is routinely overlooked. A profile can be within limits on every cross-sectional dimension and still be unusable.
| Group | What is controlled | Where it shows |
|---|---|---|
| Dimensions | Width, height, wall thickness | Sliding into a groove, cap seating |
| Straightness | Bow along the length of the bar | Continuous runs, exposed edges |
| Twist | Rotation of the section about its axis | Frames, parts fixed at both ends |
| Angles and shape | Squareness, flatness of walls | Corner joints, mating faces |
Of these, twist is the one that generates most complaints. It develops as the section cools after extrusion and is most pronounced in thin-walled or asymmetric shapes.
On a two metre bar it is barely visible. On a six metre bar it is obvious, and it can be obvious while the profile still conforms to the standard. That is the uncomfortable part: conforming and convenient are not the same thing.
Checking a delivery in three steps
Incoming inspection of a profile does not need a measuring room. A vernier caliper and a flat surface will settle most questions.
- Measure the section at both ends of the bar, not at one. The difference between the ends tells you more than a single reading somewhere inside the tolerance band.
- Check straightness by laying the bar on a flat surface. The gap under the middle of its length shows bow faster than any instrument.
- Check twist by rotating the bar on that same surface. If one end lifts, the section is twisted.
If the inspection does find a problem, the decisive question is what the material is being measured against. Without a tolerance standard on the order, the supplier and the customer are left arguing about what counts as acceptable, and nothing in the paperwork settles it.
That is the practical reason to name the standard even when it feels self-evident.
Press fit is a different question
One question comes up often enough to be worth separating out: what press fit tolerance applies to aluminium.
Product tolerance and fit are two different systems. EN 755-9 and EN 12020-2 tell you how far the delivered profile may deviate from its nominal size. A press fit is a design decision about the intended interference between two mating parts, and it belongs to the drawing, not to the material standard.
The two do interact. The fit has to work across the whole tolerance band of the delivered section, not just at its nominal dimension, and aluminium expands roughly twice as much as steel for the same temperature change. A fit designed at the nominal size can go slack at one end of the band and seize at the other.
Where an interference fit is critical, machining the mating feature after delivery is more reliable than specifying an extrusion tolerance tight enough to carry the fit on its own.
Where twist and bow come from
Understanding the cause makes the limits easier to accept.
A profile leaves the press hot and is cooled at the exit. Uneven wall thickness means uneven cooling, and uneven cooling means internal stress. The section is then stretched to straighten it. That removes most of the stress, but never all of it.
This is why the wall ratio limit sits in EN 12020-2 in the first place, and why an asymmetric section will always be harder to hold straight than a symmetric one. The full sequence is described in the guide to how aluminium profiles are made.
Two design habits reduce the problem before it starts: keep wall thicknesses as even as the function allows, and avoid long thin flanges hanging off a heavy body.
What to put on the order
Most tolerance disputes trace back to an order that never mentioned tolerance. Five lines prevent nearly all of them:
- Alloy and temper, for example EN AW-6063 T6. The words aluminium profile on their own are not a specification.
- Section dimensions including wall thickness, in millimetres.
- The tolerance standard, EN 12020-2 for precision sections in 6060 and 6063, EN 755-9 otherwise.
- Which dimension is critical, if one of them is. A profile that fits a groove has one dimension that matters more than the rest.
- Whether you need a 3.1 inspection certificate under EN 10204, as explained in the guide to material certificates.
The third line is the one that goes missing most often, and it is the one that decides whether the part fits on site.
Aluminium profiles from ULAMEX
ULAMEX supplies extruded aluminium profiles and sections from stock in Zawada, Poland, to customers across continental Europe. The range and the selection criteria are covered in the guide to aluminium profiles.
Tolerance data for the standard that applies to a delivered section is available on request and traceable to the shipment, so a query from an architect or a main contractor can be answered the first time it is asked. A 3.1 inspection certificate under EN 10204 is available on request as well.
Welded load-bearing structures fabricated by ULAMEX carry CE marking to EN 1090-1 EXC2, with welding under an ISO 3834-2 quality system. The company has traded in steel and aluminium since 1988, that is 38 years. There is no minimum order on stocked SKUs and delivery within continental Europe usually takes 2 to 7 working days.
Send the section, alloy, tolerance standard and quantity to our contact page and we will come back with a non-binding quotation.
Frequently asked questions
What are the standard tolerances for aluminium extrusions?
They depend on which of two standards applies. EN 755-9 covers extruded profiles for general engineering, with a cross section fitting inside a circumscribing circle of up to 800 mm, and it grades its tolerances by alloy group. EN 12020-2 covers precision profiles in EN AW-6060 and EN AW-6063, with tighter limits and stricter requirements on visible surfaces. Two profiles of identical catalogue size can therefore carry different guaranteed accuracy.
When does EN 12020-2 apply instead of EN 755-9?
Four conditions have to be met at the same time: the alloy is EN AW-6060 or EN AW-6063, the circumscribing circle is 350 mm or less, the mass is 10 kg/m or less, and the ratio of the thickest to the thinnest wall is 3.5 or less. Failing any one of them puts the section back under EN 755-9. The wall ratio limit exists because a section combining heavy and very thin walls cools unevenly and distorts.
Do tolerances cover more than the cross-section dimensions?
Yes. Both standards address dimensions and form, and form is the half that gets overlooked. It covers straightness along the bar, twist about the axis, squareness of angles and flatness of walls. A profile can be within limits on every cross-sectional dimension and still be difficult to use because it is bowed or twisted.
Why is a profile twisted even though it meets the standard?
Twist develops as the section cools after extrusion, and it is most pronounced in thin-walled or asymmetric shapes. On a two metre bar it is barely visible; on a six metre bar it is obvious, and it can be obvious while the profile still conforms. Conforming to the standard and being convenient to work with are not the same thing.
How do I check a delivered profile without measuring equipment?
A vernier caliper and a flat surface cover most of it. Measure the section at both ends of the bar rather than at one, because the difference between the ends is more informative than a single reading. Lay the bar on the flat surface and look at the gap under the middle of its length to see bow. Rotate it on the same surface to see twist: if one end lifts, the section is twisted.
Does the alloy affect the tolerance?
Within EN 755-9 it does. The standard sorts alloys into two groups by how difficult they are to extrude, and the tolerance tables differ between the groups, with the harder higher-strength alloys allowed wider limits. Changing a section from an easily extruded grade to a stronger one can therefore widen the tolerance the supplier has to hold, on the same drawing and the same nominal dimensions.
What press fit tolerance should I use for aluminium?
Product tolerance and fit are separate systems. EN 755-9 and EN 12020-2 state how far a delivered profile may deviate from nominal size, while a press fit is a design decision about interference between mating parts and belongs on the drawing. The fit has to work across the whole tolerance band, not only at nominal, and aluminium expands roughly twice as much as steel for the same temperature change. Where interference is critical, machine the mating feature after delivery.
What should the order state to avoid a tolerance dispute?
Alloy and temper, section dimensions including wall thickness, the tolerance standard, which dimension is critical if one of them is, and whether a 3.1 inspection certificate under EN 10204 is required. The tolerance standard is the line that goes missing most often, and without it there is nothing in the paperwork to settle what counts as acceptable.