Aluminium Guide · Lesson 07

Tolerances and standards: EN 755 made simple

No profile comes out exactly to the dimensions on the drawing. Standards set how far it may deviate, and knowing this avoids surprises in assembly and in weight.

4 minutes’ read

In short

Tolerance is how much the actual dimension may differ from the one on the drawing. Each standard sets those limits.
For extruded profiles, the reference is the European EN 755 family of standards: mechanical properties (part 2) and tolerances on shape and dimensions (part 9).
The actual weight can differ from the theoretical weight because of thickness tolerances: that is why calculators give a theoretical weight.

What a tolerance is

A drawing says "2 mm wall", but extrusion has variations inherent to the process: die wear, temperature, speed. The tolerance is the accepted margin, for example "2 mm ± 0.15 mm". A profile within that margin is correct even if it does not measure exactly 2 mm.

The standards in use

Standard	What it defines
EN 755-1	Technical conditions for inspection and delivery
EN 755-2	Minimum mechanical properties for each alloy and temper (the ones used by the alloy comparison tool)
EN 755-9	Dimensional and shape tolerances for profiles
EN 12020-2	Tighter tolerances for precision profiles in 6060 and 6063

In Argentina, the industry works mostly with these European standards or with the equivalent IRAM standards. If your project or your client requires a particular standard, say so when you order.

What is checked on a profile

Cross-section dimensions: width, height and wall thicknesses.
Straightness: how much it bows along the length.
Twist: how much it twists about its axis.
Flatness and angles: faces must be flat and right angles must be square.
Cut length.

The limits depend on the size of the profile (its circumscribing circle) and on the alloy: alloys that are harder to extrude, such as 6082, have somewhat wider tolerances than 6063.

Theoretical weight and actual weight

The weight per metre in a catalogue is theoretical: it comes from the nominal cross-section multiplied by the density. Since the actual thickness can be slightly above or below nominal, the actual weight of a batch can differ by a few percent from the theoretical weight without the material being out of tolerance. Bear this in mind when comparing prices per kilo and when calculating loads.

Frequently asked questions

Which standard is used for extruded aluminium profiles?

The EN 755 family: part 2 defines the mechanical properties and part 9 the dimensional and shape tolerances. For precision profiles in 6060 and 6063, EN 12020-2 is used.

Why does the actual weight of a profile differ from the catalogue weight?

Because the catalogue gives the theoretical weight, calculated from the nominal dimensions. The actual thickness varies within the tolerance of the standard, and so does the weight.