Welding
TIG or MIG with ER4043 or ER5356 filler. Welded 6xxx tube loses strength near the weld; place welds away from peak stress or use bolted gussets.
Hollow sections
Aluminium Square Tube
Aluminium square tube, also called square hollow section or box section, is a hollow extrusion with four equal sides, specified by outside size, wall thickness and corner radius. It gives high bending and torsional stiffness for its weight and is easy to join with flat faces. Metline supplies square tube in 6063, 6061 and 6082 and other grades, in mill, anodised or powder-coated finish, to customers worldwide.
- Sizes
- about 10 – 250 mm square
- Wall
- about 1 – 12 mm
- Main grades
- 6063-T5/T6, 6061-T6, 6082-T6
- Standards
- ASTM B221 · EN 755-2 · EN 755-8
What is aluminium square tube?
Square tube combines the stiffness of a hollow section with flat faces that make drilling, fastening, welding and cladding straightforward. It is the backbone of frames for machines, vehicles, furniture, display systems, solar structures and architectural features. Almost all square tube is extruded, normally on porthole (bridge) dies, which means it contains longitudinal extrusion welds that are fully acceptable for structural and general use.
Three dimensions define a square tube: the outside width (A × A), the wall thickness (t) and the corner radius. Architectural tube tends to have small, crisp outer corners; structural box sections often have larger outer and inner radii, which spreads stress and improves extrusion. Drawn square tube, made by cold drawing an extruded tube, is available in smaller sizes when tighter tolerance and a smoother finish are required.
For sizes, colour and tolerance requirements beyond the standard range, custom dies are inexpensive compared with steel tooling, so non-standard walls, internal ribs or screw ports can be built into the section. See custom extrusions.
Square tube grades and typical properties
| Grade and temper | Typical tensile | Typical yield | Best for |
|---|---|---|---|
| 6063-T5 | 186 MPa | 145 MPa | Architectural frames, furniture, display systems; best anodised surface |
| 6063-T6 | 241 MPa | 214 MPa | Frames needing a little more strength with a decorative finish |
| 6061-T6 | 310 MPa | 276 MPa | Structural frames, vehicle and trailer parts, machined tube |
| 6082-T6 | about 310 MPa (EN 755-2 min. for t > 5 mm) | about 260 MPa (min.) | European structural sections, scaffolding, bridges and walkways |
| 6005A-T6 | about 255 – 270 MPa (min.) | about 215 – 225 MPa (min.) | Thin-wall structural tube, rail and bus frames |
| 7075-T6 / 2024-T3 | 480 – 570 MPa | 345 – 500 MPa | Aerospace and high-performance sports parts (drawn tube) |
Typical values from Aluminum Association and ASM data; minimums from EN 755-2 depend on wall thickness. For welded structures, design to the reduced heat-affected-zone strength given in Eurocode 9 (EN 1999-1-1) or the Aluminum Design Manual.
Square tube sizes and weight per metre
Supply range
- Outside size
- about 10 × 10 mm to 250 × 250 mm; larger by custom die
- Wall thickness
- about 1 – 12 mm depending on size
- Imperial sizes
- 1/2 in to 8 in square; walls 1/16, 1/8, 3/16, 1/4 in
- Lengths
- 5.8 m, 6 m, 6.5 m, 12 ft and 20 ft; cut lengths to order
- Finish
- Mill, clear or colour anodised, powder coated, brushed
- Processing
- Cutting, mitring, drilling, punching and CNC machining on request
Weight in kg/m ≈ 0.0108 × t × (A − t), with A and t in millimetres (density 2.70 g/cm³, sharp corners). Rounded corners reduce the weight slightly. Use the tube weight calculator for other sizes.
| Size A × A (mm) | Wall t (mm) | kg per metre | kg per 6 m |
|---|---|---|---|
| 10 × 10 | 1 | 0.097 | 0.58 |
| 15 × 15 | 1.5 | 0.219 | 1.31 |
| 20 × 20 | 1.5 | 0.300 | 1.80 |
| 20 × 20 | 2 | 0.389 | 2.33 |
| 25 × 25 | 2 | 0.497 | 2.98 |
| 25.4 × 25.4 | 3.18 | 0.763 | 4.58 |
| 30 × 30 | 2 | 0.605 | 3.63 |
| 40 × 40 | 2 | 0.821 | 4.92 |
| 40 × 40 | 3 | 1.199 | 7.19 |
| 50 × 50 | 3 | 1.523 | 9.14 |
| 50.8 × 50.8 | 3.18 | 1.635 | 9.81 |
| 60 × 60 | 4 | 2.419 | 14.52 |
| 76.2 × 76.2 | 6.35 | 4.790 | 28.74 |
| 80 × 80 | 4 | 3.283 | 19.70 |
| 100 × 100 | 5 | 5.130 | 30.78 |
| 120 × 120 | 6 | 7.387 | 44.32 |
| 150 × 150 | 8 | 12.269 | 73.61 |
| 200 × 200 | 10 | 20.520 | 123.12 |
Standards, tolerances and inspection
| Standard | Covers |
|---|---|
| ASTM B221 / B221M | Extruded tube and hollow profiles; tolerances per ANSI H35.2 |
| ASTM B429 | Extruded structural pipe and tube |
| EN 755-2 | Mechanical properties of extruded tube and profiles |
| EN 755-8 | Tolerances for porthole tubes, including square |
| EN 755-7 / EN 754-7 / EN 754-8 | Seamless and drawn tube tolerances |
| EN 12020-2 | Tolerances for precision 6060/6063 profiles (architectural) |
| EN 1999 (Eurocode 9) | Structural design of aluminium structures |
Tolerances cover outside size, wall thickness, corner radii, convexity or concavity of the faces, twist, straightness and squareness of cut ends. Architectural tube to EN 12020-2 is held tighter than general tube to EN 755-8. Every delivery is checked for dimensions and surface and supplied with an EN 10204 3.1 certificate.
Joining, finishing and design tips
Mechanical joints
Corner keys, internal connectors, rivnuts and self-drilling screws make frames without welding and keep finishes intact.
Bending
Square tube wrinkles and distorts on tight bends; use generous radii, mandrels or fillers, and form in T4 where possible.
Anodising
6063 gives the most uniform colour. Order anodising-quality extrusions and avoid mixing lots on visible frames.
Powder coating
Durable and available in any colour; pretreatment with chromate-free conversion coating gives the best adhesion.
Stiffness
For the same weight, a larger tube with a thinner wall is stiffer than a small, thick one, but keep width-to-wall ratios moderate to avoid local buckling.
Where aluminium square tube is used
- Machine and automation frames: guards, bases, conveyor frames, workstations
- Building and architecture: balustrades, pergolas, louvres, curtain-wall mullions, partitions
- Transport: trailer and truck body frames, bus and rail interiors, ramps
- Solar and outdoor structures: mounting rails, carports, greenhouses, signage frames
- Furniture and retail: tables, shelving, exhibition stands, display systems
- Marine: T-tops, rails and frames in 6061 or 6082, anodised or painted
How to order square tube from Metline
- SpecifyGrade and temper, outside size, wall, corner style, finish, length, quantity and the governing standard.
- QuoteWe confirm alloy, temper, tolerances, certification, packing and delivery terms (EXW, FOB, CIF or DAP) for your destination.
- ProcessTubes are cut and machined where ordered, checked for size, wall, twist and straightness, and protected with film or sleeves for finished surfaces.
- DocumentEach delivery carries a mill test certificate to EN 10204 3.1 with the cast analysis and mechanical results; third-party inspection can be arranged on request.
- ShipBundled, interleaved or crated for export and shipped by sea or air on EXW, FOB, CIF or DAP terms.
References and standards
- ASTM B221 – Standard Specification for Aluminum and Aluminum-Alloy Extruded Bars, Rods, Wire, Profiles, and Tubes
- ASTM B429 – Standard Specification for Aluminum-Alloy Extruded Structural Pipe and Tube
- EN 755-2 and EN 755-8 – Extruded tubes: mechanical properties and porthole tube tolerances
- EN 1999-1-1 (Eurocode 9) – Design of aluminium structures
- The Aluminum Association – Aluminum Design Manual
Aluminium (aluminum) square tube: frequently asked questions
What is the difference between 6063 and 6061 square tube?
6063 has a smoother surface and anodises more evenly, making it the choice for architectural and decorative frames. 6061-T6 is about 30 % stronger in yield and is used for load-bearing and machined structures.
How do I calculate the weight of aluminium square tube?
Weight (kg/m) ≈ 0.0108 × wall × (side − wall), dimensions in millimetres. A 50 × 50 × 3 mm tube weighs about 1.52 kg per metre; rounded corners make it slightly lighter.
Is extruded square tube seamless?
Usually not. Square tube is normally extruded on porthole dies and contains longitudinal extrusion welds, which are fully bonded and suitable for structural use. Seamless square tube is a special product for pressure or critical service.
Can aluminium square tube be welded?
Yes, 6063, 6061 and 6082 square tube weld well by TIG or MIG. The heat-affected zone loses part of its T6 strength, which structural codes account for.
Can you supply square tube anodised or powder coated?
Yes. Square tube can be supplied mill finish, anodised in clear or colour, or powder coated, and cut to length, with certificates and export packing.
Need aluminium square tube?
Send grade, size, wall, finish, length and quantity. We will reply with availability, certification and a delivered price.
