Aluminium Square Tube: Sizes, Weights, Alloys and Selection

What is aluminium square tube?

Square tube (also called square tubing, square hollow section, SHS or box section) is a closed profile with equal outside width and height. Because the material sits far from the neutral axis on all four faces, it resists bending and twisting much better than a solid bar or an open angle of the same weight.

Almost all aluminium square tube is extruded: a heated billet is pushed through a porthole or bridge die, the metal splits around a mandrel and rejoins inside the die to form the hollow. This produces fine longitudinal seam welds that are metallurgically sound and fully acceptable for structural use under ASTM B221 and EN 755. Where a design or code calls for a tube with no seam, for example some pressure or hydraulic applications, seamless tube is extruded over a piercing mandrel or drawn, which costs more and limits the size range.

Square tube is described by outside width × outside width × wall thickness, for example 50 × 50 × 3 mm or 2 × 2 × 1/8 in. Corners may be sharp (a small outside radius only) or radiused. Sharp-corner tube is common in architectural and furniture work; generous radii improve metal flow, reduce stress concentration and are typical of heavier structural sections.

Which alloy and temper for square tube?

Six alloys cover nearly every square tube requirement. The first decision is whether the tube is mainly structural (choose 6061, 6082 or 6005A) or mainly appearance-led (choose 6063 or 6060). The values below are typical properties for extrusions; design to the specified minimums in ASTM B221 or EN 755-2, which depend on wall thickness and are reported on the mill certificate.

Specified minimums for 6061-T6 extruded tube in ASTM B221 are 260 MPa (38 ksi) tensile and 240 MPa (35 ksi) yield, which is why some catalogues quote 35 ksi rather than the typical 40 ksi.

Stronger aerospace alloys are also extruded as square tube. 2024-T3/T351 offers high fatigue strength and 7075-T6 the highest static strength, but both are poor for welding and less corrosion-resistant, so they are used only where a specification calls for them. 5052 and 3003 square tube exist in small sizes for marine trim and general fabrication where formability and corrosion resistance matter more than strength.

Metric square tube sizes, weights and section properties

The table lists commonly extruded metric sizes. Weight, area, second moment of area (I) and elastic section modulus (Z) are calculated from the nominal sharp-corner section at a density of 2.70 g/cm³; corner radii reduce them slightly. Use them for estimating and for first-pass sizing, then confirm with the supplier's drawing for the exact die.

Larger sections, 250 mm and above, are produced on large extrusion presses as custom profiles, often with internal webs or radiused corners. For quick weights of any size use the aluminium tube weight calculator.

Inch square tube sizes (1/2 in to 8 in)

North American buyers usually order square tubing in fractional inches, with the wall given as a fraction or gauge (1/16 in is close to 16 gauge, 1/8 in close to 10 gauge). Weights are calculated for sharp corners.

Typical mill lengths are 6 m in metric markets and 20 ft or 24 ft in inch markets; shorter lengths such as 8 ft, 3 m or exact cut lengths are cut from these. Long lengths reduce joints in a frame but raise freight cost for container shipments, so confirm what fits the route.

How to choose size and wall thickness

For the same weight, a larger tube with a thinner wall is stiffer than a smaller tube with a thick wall, because stiffness rises with the cube of the width. That is why 50 × 50 × 2 mm (1.04 kg/m, I = 14.8 cm⁴) is about 45 % stiffer in bending than 40 × 40 × 3 mm (1.20 kg/m, I = 10.2 cm⁴), even though it is lighter. The limit is local buckling: very thin walls crumple or dent before the tube reaches its yield strength.

1. Start from the load caseWork out the bending moment, axial load and allowable deflection. Aluminium has about one third of the elastic modulus of steel (about 69 GPa), so deflection usually governs before strength.
2. Pick a width for stiffnessUse the I values above to find the smallest section that meets the deflection limit, then check stress using Z and the design strength of the alloy.
3. Check wall slendernessKeep the face width-to-thickness ratio (b/t) moderate for members in compression or bending. Design codes such as the Aluminum Design Manual and EN 1999-1-1 (Eurocode 9) classify sections by b/t and reduce allowable stress for slender walls.
4. Allow for weldingWelding 6xxx tube softens a band about 25 mm wide around the weld. Eurocode 9 and the Aluminum Design Manual give reduced heat-affected-zone strengths; place welds away from the highest-stress point where possible.
5. Think about jointsThicker walls hold threads, rivnuts and self-tapping screws better. If the frame uses bolted joints through the tube, check bearing and crushing at the holes or add sleeves.

Tolerances, straightness and inspection

Square tube is supplied to the tolerance tables of the ordering standard unless the drawing tightens them. Outside width tolerance depends on size and on whether it is measured at the corners or mid-face; wall thickness tolerance is usually a percentage of nominal wall, and seamless tube is held tighter than porthole tube.

• Dimensional check of width, wall, corner radius, length, straightness and twist
• Visual surface inspection, more stringent for anodising-quality 6063
• Tensile and hardness testing per lot; chemistry by spectrometer
• Mill test certificate to EN 10204 3.1 with every shipment; third-party inspection on request

Surface finishes and fabrication

Where aluminium square tube is used

• Building and architecture: balustrade posts, partitions, sub-frames, pergola members and support structures for cladding, using 6063 or 6060 profiles supplied to fabricators
• Machinery and automation: machine bases, guards, conveyor frames and workbenches, mainly 6061-T6 and 6082-T6
• Transport: trailer and truck body frames, bus and rail interior structures, roof racks and ladders
• Marine: boat frames, T-tops, rails and deck furniture, anodised or painted, often in 6061-T6
• Solar and outdoor: mounting frames, equipment platforms and enclosures where corrosion resistance and low weight cut installation cost
• Furniture, retail and exhibitions: shelving, display racks, stands and frames in thin-wall 6063

A typical light-industrial workstation, for example, is built from 40 × 40 × 3 mm 6061-T6 tube with bolted corner brackets, while a balustrade might use 50 × 50 × 2 mm 6063-T5 posts that are anodised after cutting.

Aluminium square tube compared with steel

Because aluminium is about three times less stiff, a straight swap of the same size usually deflects about three times as much. Designers normally choose a larger or thicker aluminium section, which still ends up roughly half the weight of the steel member it replaces. The full life-cycle cost, including no painting or galvanising and lower transport and handling cost, is often lower than steel even though aluminium costs more per kilogram.

Related square tube products and guides

Alloy-specific square tube pages, other hollow sections and the matching tooling guide:

How to order aluminium square tube

1. SpecifySize (B × B × t), corner type, alloy and temper, standard (ASTM B221, EN 755-2), length or cut lengths, quantity and finish.
2. QuoteWe confirm the die and availability, tolerances, certification and delivery terms (EXW, FOB, CIF or DAP).
3. ProcessCutting, drilling, anodising or powder coating are arranged before packing if required.
4. DocumentMill test certificate to EN 10204 3.1, packing list and any third-party inspection report.
5. ShipBundled with paper or film interleaving and packed in wooden crates or on pallets for sea or air freight.

Aluminium (aluminum) square tube: frequently asked questions