Aluminium Flat Bar Die Sizes & Size Chart

What a flat bar die is and why size choice matters

A flat bar die is a hardened tool-steel disc, usually H13 hot-work steel, with a precisely machined rectangular aperture. The billet, heated to roughly 450 – 500 °C, is forced through it by the press ram and emerges as a continuous bar with the cross-section of the opening. Because the opening defines both thickness and width, a 6 × 40 mm bar and a 6 × 45 mm bar need two different dies.

Flat bar dies are "solid" dies: they have no mandrel or bridge, unlike the porthole dies used for hollow tube. That makes them among the simplest and cheapest extrusion tools. Even so, a new die has to be designed, machined, heat-treated, nitrided and trial-run before production metal is accepted, and the first trial frequently needs correction of the bearing lengths to get the bar flat and straight. That process adds cost and calendar time to a first order.

Extruders therefore keep libraries of existing flat bar dies in the sizes the market asks for most. When a designer picks a thickness and width that is already in a library, the order can go straight to production. When the size is new, the buyer typically pays a one-time die charge, and the die then becomes reusable for repeat orders. Small differences, such as 38 mm instead of 40 mm, can decide whether a size runs from an existing tool or needs a new one.

How flat bar is extruded, straightened and aged

1. Billet preparationHomogenised logs of the chosen alloy are cut to billet length and heated in an induction or gas furnace. 6063 and 6060 run at the lower end of the temperature range; 6061, 6082 and the hard alloys need tighter temperature control.
2. Die heating and loadingThe flat die is pre-heated so that it does not chill the metal, then locked into the die stack in front of the container.
3. ExtrusionThe ram pushes the billet through the die. Exit speed depends on alloy and section: soft 6063 flats can run quickly, while 2024 and 7075 are extruded far more slowly to avoid surface tearing.
4. QuenchingHeat-treatable alloys are quenched at the press exit by air or water spray so that they can later reach full T5 or T6 strength. Thick flats in 6061 and 6082 need water quenching to reach T6 properties through the section.
5. StretchingEach length is gripped at both ends and stretched by about 1 – 3 %. This straightens the bar, removes twist and relieves residual stress, which is what the "51" in T6511 or T651 indicates.
6. Cutting and ageingBars are sawn to length and artificially aged in a furnace to reach T5 or T6. Samples from the batch are tested for hardness or tensile properties before release.
7. Finishing and packingMill-finish bars are interleaved and bundled; anodised or powder-coated bars are finished after ageing and then wrapped to protect the surface.

Cold-drawn flat bar is a separate product: an extruded bar is drawn through a carbide die at room temperature to tighten tolerances and improve surface finish. Cold-drawn bar is covered by EN 754-5 in Europe and is normally limited to smaller sections; most structural and general-purpose flats are supplied as-extruded.

Metric aluminium flat bar sizes and weights (2 – 50 mm thick)

The sizes below are widely produced metric flat bar dimensions. Weights are theoretical, calculated from a density of 2.70 g/cm³ (6061, 6082 and 6063 are within about 1 % of this). For 2024 multiply by about 1.03 and for 7075 by about 1.04. Size is thickness × width in millimetres.

Whether a given size can run from an existing die depends on the extruder and the alloy; confirm when you request a quote. Widths above about 250 mm and thicknesses above 50 mm are usually supplied by larger presses or cut from plate.

Inch (imperial) aluminum flat bar sizes and weights

North American drawings normally call up fractional-inch flat bar to ASTM B221. The table shows common fractional sizes with the metric equivalent, the weight in pounds per foot (based on 0.0975 lb/in³) and the converted weight in kilograms per metre.

Some inch sizes are close to metric ones but not identical: 1/4 × 1 in is 6.35 × 25.4 mm, not 6 × 25 mm. If your drawing is in inches, quote the inch size so the bar is extruded from an inch die rather than substituted from the nearest metric die; the difference matters when the bar fits into a slot or mates with an inch fastener pattern.

How to calculate flat bar weight

Flat bar weight is simple geometry. Multiply the cross-sectional area by the density and the length. Corner radii reduce weight slightly, but on most flats the effect is well under 1 % and is ignored for ordering purposes.

For any other size, use the aluminium bar weight calculator. When estimating freight, add the weight of packing: wooden cases or pallets and interleaving typically add a noticeable margin to the net metal weight.

Size limits: circle size, press capacity and width-to-thickness ratio

Three things decide whether a flat bar size can be extruded and how easily: the circumscribing circle diameter (CCD), the press force and the shape factor.

As a rule, flats up to around 150 mm wide are easy to source in all common alloys. Between about 150 mm and 300 mm, choice narrows and larger presses are needed. Beyond that, buyers often compare a wide extruded flat with a strip sawn from 6061 plate, which may be faster and offers wider thickness choice.

Alloys and tempers for extruded flat bar

Typical tensile strengths give a feel for the range: 6063-T6 is about 240 MPa, 6061-T6 about 310 MPa, 2024-T3 about 480 MPa and 7075-T6 about 570 MPa (Aluminum Association typical values). Specified minimum values for extruded bar are lower and vary with thickness; they are set by ASTM B221 and EN 755-2 and are reported on the mill certificate.

T5 means cooled from the extrusion temperature and artificially aged; T6 means solution heat-treated (or press-quenched to an equivalent condition) and artificially aged. T6511 adds controlled stretching and minor straightening, which makes the bar more stable when machined.

Tolerance standards for extruded flat bar

Flat bar tolerances are not a single number: they depend on the width band, the thickness band and the alloy group. Harder alloys such as 2024 and 7075 (Group II in the EN system) have wider tolerances than 6060, 6063 and 6082 (Group I), because they are harder to control at the press.

The standards control thickness, width, corner radius, flatness (concavity and convexity across the width), straightness along the length, twist and squareness of the cut ends. Where a drawing needs tighter values than the standard gives, state them explicitly on the order: for example a ground or milled thickness, a precision-sawn length, or a straightness limit per metre. Tighter limits are achievable by machining or by selecting bars, at extra cost.

Two practical points avoid disputes. First, measure thickness away from the corners, because the corner radius is not part of the flat dimension. Second, check straightness and twist with the bar lying under its own weight on a flat table, which is how the standards define them.

Surface finishes for flat bar

Cutting, bending, punching and machining flat bar

• Cut to length: standard lengths are often 3 m, 4 m or 6 m (or 12 ft and 20 ft); precision sawing to a tighter length tolerance is available on request.
• Bending: easiest in 6063-T5 and in T4 tempers; 6061-T6 and 6082-T6 need larger radii. Bending the flat the "easy way" (about the thin axis) is far simpler than edgewise bending.
• Punching and slotting: holes and slots should keep at least about one thickness, and preferably more, from the edge to avoid bulging or tearing.
• Welding: MIG or TIG with ER4043 or ER5356 filler for 6xxx flats; heat-treated tempers lose strength in the heat-affected zone. 2024 and 7075 are not fusion-welded in structural work.
• Machining: allow a machining margin on sawn faces if a finished dimension matters; T6511 bar moves less when one face is machined.
• Anodising after fabrication: anodise after bending, drilling and welding where possible; weld zones in 6xxx may anodise to a different shade.

How to order flat bar from Metline

1. SpecifyAlloy and temper, thickness × width (state metric or inch), length, quantity, finish and governing standard (ASTM B221, EN 755-2/-5).
2. Confirm the sizeWe confirm whether the size is a standard section or needs a new die, and suggest the nearest standard alternative where it would save cost.
3. QuotePrice, tolerance class, certification and delivery terms (EXW, FOB, CIF or DAP) for your destination.
4. Process and inspectCutting, finishing and dimensional inspection; EN 10204 3.1 mill certificate with chemistry and mechanical results.
5. Pack and shipBundled with interleaving or film, in wooden cases or on pallets, and shipped worldwide by sea or air.

Related flat bar and extrusion pages

Aluminium flat bar die sizes: frequently asked questions