Aluminium Rectangular Tubing: A Practical Buyer's Guide

What rectangular tubing is and why engineers use it

A rectangular tube puts most of its metal far from the neutral axis in the deep direction. For the same weight it is much stiffer and stronger in bending about its strong axis than a square or round tube, which is why it is used for beams, chassis rails, gantry members and frame sides.

Almost all aluminium rectangular tubing is extruded. Standard architectural and structural sizes are made in porthole dies, which form solid-state seam welds along the length; these are sound for structural use. Where a truly seamless tube is required, for example for pressure or some aerospace uses, rectangular tube can be drawn from seamless round tube, but this is a specialist and more expensive route.

Flat faces make rectangular tube easy to join: it bolts, rivets and welds flat against plates and other members, accepts T-slot and clamp hardware, and gives a clean, modern look in furniture, shopfitting and architecture. The choice between sharp-corner and radiused-corner tube is mostly aesthetic and practical: sharp corners mate neatly with other flat parts, while radiused corners coat more evenly and are kinder to hands.

Choosing the alloy and temper

6063 and 6061 values are specified minimums from ASTM B221 for extruded tube. Some catalogues quote 6061-T6 at 290 MPa tensile and 6063-T5 at 190 MPa; those figures belong to rolled sheet or are typical rather than guaranteed values. Design to the specified minimum and check the mill certificate.

For most buyers the decision is between 6063 and 6061. Pick 6063 when appearance, anodising and cost drive the choice and loads are modest. Pick 6061-T6 when the tube carries real structural load, is welded into a frame, or must resist denting. In Europe, 6082-T6 and 6005A-T6 fill the role that 6061-T6 plays elsewhere.

Inch rectangular tubing: weights and bending properties

Values are calculated for sharp outside corners and a density of 2.70 g/cm³. I and W are about the strong axis, that is, bending with the height vertical. Radiused-corner tube has slightly lower area and stiffness.

Calculated from nominal dimensions. Weights in lb/ft are kg/m × 0.672.

Metric rectangular tubing: weights and bending properties

Smaller and intermediate metric sizes are listed with weights in the rectangular tube die sizes guide, which also explains which sizes need new tooling. For very large sections up to 1200 mm, see extra-large square and rectangular tube.

Rectangular, square or round tube?

As a quick example from the metric chart: a 50 × 100 × 3 mm rectangular tube weighs about 2.33 kg/m and has a strong-axis section modulus of about 22 cm³ and a moment of inertia of about 112 cm⁴. A 75 × 75 × 3 mm square tube of exactly the same weight has a section modulus of about 20 cm³ and a moment of inertia of about 75 cm⁴. If the load is mainly vertical, the rectangular tube is around 10 % stronger and 50 % stiffer for the same metal.

Sizing a rectangular tube beam: a worked example

Because aluminium's modulus of elasticity (about 69 GPa) is roughly one third of steel's, an aluminium beam sized only for strength often deflects more than the design allows. In most frames and platforms, stiffness governs, so check deflection first and stress second.

1. Define the load caseExample: a 2 m simply supported beam carrying a 1 kN point load at mid-span, using 50 × 100 × 3 mm tube in 6061-T6 with the 100 mm side vertical.
2. Check bending stressBending moment M = P × L / 4 = 500 N·m. With a section modulus of about 22.4 cm³, the bending stress is about 22 MPa, a small fraction of the 240 MPa minimum yield.
3. Check deflectionDeflection = P × L³ / (48 × E × I) = 1000 × 2000³ / (48 × 69 000 × 1 121 000) ≈ 2.2 mm, or about span/930. That satisfies a typical span/250 or span/360 limit comfortably.
4. OptimiseWith so much margin, a thinner wall or a 6063-T6 tube may work. Turning the same tube on its side (50 mm vertical) would cut stiffness by about two thirds, so orientation matters as much as size.
5. Allow for welds and holesIf the beam is welded near mid-span, or drilled through the flanges, reduce the allowable stress accordingly and check the local area.

• Common mistake: designing an aluminium frame by copying steel sizes. Equal deflection usually needs a deeper section, not just a thicker wall.
• Common mistake: using catalogue "typical" strengths for design. Use specified minimums from ASTM B221 or EN 755-2.
• Common mistake: ignoring local wall crushing at supports and bolt points; add crush tubes, bearing plates or a thicker wall.
• Common mistake: using 6063-T5 for a welded structural frame where 6061-T6 or 6082-T6 was needed.

Tolerances, straightness and inspection

If your design relies on a sliding fit, such as telescoping tubes, specify the critical dimensions and ask for a fit check, because the standard tolerances of two separate sizes can add up to more clearance than you expect.

For decorative work, also state which faces are visible. Extrusion die lines and seam welds can show through a clear anodised finish, and the die and handling can be arranged to keep them on hidden faces when this is agreed in advance.

Cutting, bending, welding and finishing

Where aluminium rectangular tubing is used

• Transport: trailer and truck body frames, rail vehicle interiors, bus structures, EV battery tray frames.
• Industrial equipment: machine guards, conveyor frames, gantries, linear-motion supports, inspection platforms.
• Building and architecture: mullions, louvres, pergolas, balustrade posts, partitions and signage frames.
• Marine: boat rails, gangways, pontoon frames and walkways, usually in 6061-T6 or 5xxx alloys.
• Solar and energy: mounting rails and support frames for photovoltaic arrays.
• Furniture and retail: tables, shelving, display systems and lightweight frames.
• Aerospace and defence: ground-support equipment, shelters and drawn high-strength tube for secondary structure.

How to order rectangular tubing from Metline

1. SpecifyAlloy and temper, width × height × wall, corner style, length, quantity, standard and finish.
2. QuoteWe confirm whether the size runs on existing tooling, the tolerances, certification and delivery terms (EXW, FOB, CIF or DAP).
3. ProcessTubes are cut, machined, finished or protected with film as ordered and inspected for dimensions and surface.
4. Document and shipEach shipment includes the EN 10204 3.1 certificate and packing list; tubes are bundled with protective wrapping and packed in wooden cases or crates for export.

Related rectangular tube and tooling pages

Aluminium (aluminum) rectangular tubing: frequently asked questions