Mill finish
As extruded. Economical for hidden structures or parts that will be welded and painted.
Square and rectangular hollow sections
Aluminium Box Section
Aluminium box section is a square or rectangular hollow extrusion: a closed tube with flat faces that gives high bending and torsional stiffness for its weight. Metline supplies box sections from 12.7 × 12.7 mm (½ in) up to 200 × 200 mm, with walls from about 1.2 to 6 mm, in 6063, 6061, 6082 and higher-strength grades, mill finish, anodised or powder coated and cut to length for customers worldwide.
- Sizes
- 12.7 – 200 mm
- Wall
- about 1.2 – 6 mm
- Alloys
- 6063, 6061, 6082
- Lengths
- 2.5 – 6 m or cut
What is aluminium box section?
"Box section" is the British and Commonwealth name for square and rectangular hollow sections, called square tube or rectangular tube in North America. Both describe the same product: an extruded closed shape with four flat walls and small corner radii.
Placing the metal at the outside of the section is what makes a box section efficient. A 50 × 50 × 3 mm aluminium box weighs about 1.5 kg/m, yet it is roughly eight times stiffer in bending than a solid square bar of the same weight (about 24 mm square). The closed shape also resists twisting far better than an open channel or angle of the same weight, which is why box section is used for frames that see torsion: trailers, gates, furniture, ladders and machine bases.
Most aluminium box sections are extruded through porthole (bridge) dies, which split the metal around a mandrel and weld it back together inside the die. The resulting longitudinal seams are fully bonded and have no practical effect on structural use. For pressure applications or where a specification calls for it, seamless tube extruded over a mandrel from a hollow billet is available instead.
Alloys and tempers for box section
| Alloy and temper | Min. tensile | Min. yield | Strengths | Typical use |
|---|---|---|---|---|
| 6060-T6 | 190 MPa | 150 MPa | Very smooth surface, easy to bend | Trims, shopfitting, light frames |
| 6063-T5 | 175 MPa | 130 MPa | Excellent finish, economical | Windows, furniture, displays |
| 6063-T6 | 215 MPa | 170 MPa | Finish plus moderate strength | Handrails, partitions, frames |
| 6061-T6 | 260 MPa | 240 MPa | Strong, weldable, machinable | Structures, trailers, machine frames |
| 6082-T6 | 295 – 310 MPa | 250 – 260 MPa | Highest-strength common 6xxx grade | Structures, scaffolding, transport |
| 7075-T6 | about 540 MPa | about 480 MPa | Very high strength, poor weldability | Aerospace, motorsport |
Minimums for thin walls per EN 755-2 (6060, 6063, 6082) and ASTM B221 / EN 755-2 (6061); 7075 approximate. Values for thicker walls are slightly lower; the mill certificate gives actual results.
Box section sizes, weights and section properties
The table lists common metric sizes with the weight per metre and the bending properties about the major axis. Values are calculated for sharp corners from the nominal dimensions and density 2.70 g/cm³, so real profiles with corner radii are within a few per cent.
| Size B × H × t (mm) | Area (mm²) | Weight (kg/m) | Ix (cm4) | Zx (cm³) |
|---|---|---|---|---|
| 20 × 20 × 1.5 | 111 | 0.30 | 0.64 | 0.64 |
| 25 × 25 × 1.5 | 141 | 0.38 | 1.30 | 1.04 |
| 25 × 25 × 2 | 184 | 0.50 | 1.63 | 1.31 |
| 30 × 30 × 2 | 224 | 0.60 | 2.94 | 1.96 |
| 40 × 40 × 2 | 304 | 0.82 | 7.34 | 3.67 |
| 40 × 40 × 3 | 444 | 1.20 | 10.20 | 5.10 |
| 50 × 50 × 2 | 384 | 1.04 | 14.77 | 5.91 |
| 50 × 50 × 3 | 564 | 1.52 | 20.85 | 8.34 |
| 60 × 60 × 3 | 684 | 1.85 | 37.14 | 12.38 |
| 75 × 75 × 3 | 864 | 2.33 | 74.78 | 19.94 |
| 80 × 80 × 4 | 1216 | 3.28 | 117.38 | 29.35 |
| 100 × 100 × 3 | 1164 | 3.14 | 182.71 | 36.54 |
| 100 × 100 × 5 | 1900 | 5.13 | 286.58 | 57.32 |
| 150 × 150 × 5 | 2900 | 7.83 | 1017.42 | 135.66 |
| 200 × 200 × 6 | 4656 | 12.57 | 2923.35 | 292.33 |
| 40 × 20 × 2 | 224 | 0.60 | 1.44 | 1.44 |
| 50 × 25 × 2 | 284 | 0.77 | 2.96 | 2.37 |
| 60 × 40 × 2 | 384 | 1.04 | 10.23 | 5.11 |
| 80 × 40 × 3 | 684 | 1.85 | 18.43 | 9.21 |
| 100 × 50 × 3 | 864 | 2.33 | 37.44 | 14.98 |
| 120 × 60 × 4 | 1376 | 3.72 | 84.77 | 28.26 |
| 150 × 50 × 4 | 1536 | 4.15 | 68.58 | 27.43 |
| 200 × 100 × 5 | 2900 | 7.83 | 512.42 | 102.48 |
For rectangular sections, H is the dimension in the direction of the load (the "strong" axis). Ix = second moment of area; Zx = elastic section modulus. Use the rectangular tube weight calculator for other sizes.
Imperial sizes are equally common in the UK, India and North America. Walls are often given in gauge: 18 swg = 1.22 mm, 16 swg = 1.63 mm, 14 swg = 2.03 mm, 12 swg = 2.64 mm and 10 swg = 3.25 mm, or as fractions such as 1/16 in (1.59 mm), 1/8 in (3.18 mm), 3/16 in (4.76 mm) and 1/4 in (6.35 mm).
| Imperial size | Metric equivalent (mm) | Approx. weight (kg/m) |
|---|---|---|
| ½ × ½ in × 16 swg | 12.7 × 12.7 × 1.63 | 0.19 |
| ¾ × ¾ in × 16 swg | 19.1 × 19.1 × 1.63 | 0.31 |
| 1 × 1 in × 16 swg | 25.4 × 25.4 × 1.63 | 0.42 |
| 1 × 1 in × 10 swg | 25.4 × 25.4 × 3.25 | 0.78 |
| 1½ × 1½ in × 16 swg | 38.1 × 38.1 × 1.63 | 0.64 |
| 1½ × 1½ in × 10 swg | 38.1 × 38.1 × 3.25 | 1.22 |
| 2 × 1 in × 10 swg | 50.8 × 25.4 × 3.25 | 1.22 |
| 2 × 2 in × 10 swg | 50.8 × 50.8 × 3.25 | 1.67 |
| 3 × 2 in × 10 swg | 76.2 × 50.8 × 3.25 | 2.11 |
| 3 × 3 in × ¼ in | 76.2 × 76.2 × 6.35 | 4.79 |
| 4 × 2 in × 10 swg | 101.6 × 50.8 × 3.25 | 2.56 |
| 4 × 4 in × ¼ in | 101.6 × 101.6 × 6.35 | 6.53 |
| 6 × 6 in × ¼ in | 152.4 × 152.4 × 6.35 | 10.02 |
Standards and dimensional tolerances
| Region | Material and property standard | Tolerance standard |
|---|---|---|
| Europe / UK | EN 755-1, EN 755-2; chemistry to EN 573-3 | EN 755-8 (porthole tubes), EN 755-7 (seamless tubes), EN 755-9 (profiles) |
| North America | ASTM B221 (extruded tube), B241 (seamless), B429 (structural pipe and tube) | ANSI H35.2 / tolerance tables in ASTM B221 |
| India | IS 733, IS 1285 (extruded tube and hollow sections) | As per IS 1285 or the order |
| Australia / New Zealand | AS/NZS 1866 (extruded rod, bar, solid and hollow shapes) | AS/NZS 1866 |
| Structural design | EN 1999-1-1 (Eurocode 9); Aluminum Design Manual (US); AS/NZS 1664 | — |
Standard tolerances on outside dimensions, wall thickness, straightness, twist and corner radius depend on size and alloy group. As a guide, small sections are held to a few tenths of a millimetre on width and to roughly ±10 % of nominal wall, while straightness is typically held within about 1 mm per metre on general profiles. Tighter "precision" tolerances can be agreed for shopfitting, sliding fits and telescopic sections.
- State the governing tolerance standard on the order; EN and ASTM tables differ
- Telescopic (nesting) box sections need matched outside and inside tolerances, so give both sizes
- Specify corner radius if the section must fit a bracket, cap or plug
- For cut pieces, a length tolerance of ±0.5 – 1 mm is typical; tighter on request
Mill finish, anodised and powder-coated box section
Clear or colour anodised
Silver, black, bronze, champagne and other colours; 15 – 25 µm film for outdoor use.
Powder coated
White, black and any RAL colour; durable choice for furniture, railings and facades.
Brushed or polished
Mechanical finish, often clear anodised, for shopfitting and premium furniture.
Wood-grain
Sublimated wood effect over powder coat for fencing, screens and pergolas.
Protective film
PE film on visible faces to prevent marks during fabrication and installation.
Black and white box sections are among the most requested finishes. They are supplied either anodised (black only) or powder coated; powder coating gives a more uniform colour match between batches, while anodising gives a harder, thinner film that will not chip.
Cutting, bending, welding and joining box section
Cutting
Carbide-tipped circular saws with a negative-rake blade for non-ferrous metals give clean, square or mitred cuts. Laser and CNC routing suit holes and slots.
Bending
Rotary draw or mandrel bending prevents the walls from buckling. Use 6063 or 6060 in T4 or T5 for tight radii; 6061-T6 and 6082-T6 need larger radii. A guide is a centreline radius of at least 3 – 4 times the section height.
Welding
TIG or MIG with ER4043 or ER5356 filler after removing the oxide layer. The heat-affected zone of T6 sections loses roughly a third to half of its strength; account for this in design.
Mechanical joining
Blind rivets, flow-drill screws, threaded inserts, internal corner connectors and plastic or aluminium plugs give weld-free assemblies.
End caps
Plastic insert caps close open ends for safety and appearance; sizes match the outside dimension and wall.
Corrosion
Isolate box sections from steel fixings with nylon washers or use stainless fasteners with a barrier to avoid galvanic attack outdoors.
A hollow square section is stronger in bending than a solid bar of the same weight because more material sits away from the neutral axis. It is not stronger than a solid bar of the same outside size, so for very short, heavily loaded parts a solid square bar can still be the right choice.
Where aluminium box section is used
- Building and architecture: window and door subframes, curtain wall back-up members, louvres, screens and pergolas
- Structures: lightweight beams, columns, bracing, mezzanine and platform frames
- Furniture and shopfitting: table and chair frames, shelving, display stands and counters
- Transport: trailer and truck body frames, bus seat frames, roof racks and ladders
- Handrails and balustrades: posts and top rails, often powder coated
- Solar: mounting frames, rails and legs for ground and roof arrays
- Signs and exhibitions: sign frames, billboards and portable stands
- Machinery and automation: guards, carts, jigs and frames where T-slot profiles are not required
Typical example: a powder-coated 6063-T6 50 × 25 × 2 mm box is a common choice for a balcony balustrade top rail, while a 100 × 50 × 3 mm 6082-T6 box might serve as a trailer chassis member, with fully welded joints designed to the reduced weld-zone strength.
How to order aluminium box section
- SpecifyOutside size, wall thickness, alloy and temper, standard (EN 755, ASTM B221, IS 1285), finish and colour.
- QuantitiesStock lengths (commonly 2.5, 3, 5 or 6 m) or a cut list with tolerances, mitres and holes.
- QuoteWe confirm availability, tolerances, finish and delivery terms (EXW, FOB, CIF or DAP).
- InspectDimensions, straightness and finish checked; EN 10204 3.1 mill certificate supplied.
- Pack and shipFilm-wrapped, paper-interleaved bundles; short pieces in cartons; ISPM 15 crates or pallets for export.
References and standards
- EN 755-2 – Extruded rod/bar, tube and profiles: mechanical properties
- EN 755-8 – Extruded tubes using a porthole die: tolerances on dimensions and form
- ASTM B221 – Aluminum and Aluminum-Alloy Extruded Bars, Rods, Wire, Profiles, and Tubes
- ASTM B429 – Aluminum-Alloy Extruded Structural Pipe and Tube
- EN 1999-1-1 – Eurocode 9: Design of aluminium structures
- The Aluminum Association – Aluminum Design Manual
Aluminium (aluminum) box section: frequently asked questions
What is the difference between box section and square tube?
None in practice. "Box section" is the common British and Indian term for square and rectangular hollow extrusions; "square tube" and "rectangular tube" are the usual terms in North America.
How much does aluminium box section weigh?
Weight per metre equals the cross-sectional area in mm² multiplied by 0.0027. For example, 25 × 25 × 2 mm weighs about 0.50 kg/m, 50 × 50 × 3 mm about 1.52 kg/m and 100 × 50 × 3 mm about 2.33 kg/m.
Which alloy is strongest for box section?
Among standard grades, 6082-T6 is strongest, followed closely by 6061-T6. 6063 is weaker but has a better finish. For very high strength, 7075 can be supplied in limited sizes, but it cannot be welded reliably.
Can aluminium box section be bent?
Yes, with rotary draw or mandrel bending to stop the walls collapsing. Softer tempers such as 6063-T4 or T5 allow tighter radii. Send the radius, angle and section so we can advise.
How do you weld aluminium box section?
TIG or MIG with ER4043 or ER5356 filler, after cleaning off oil and the oxide layer. Expect reduced strength around the weld in T6 material and design for it.
Can you supply box section cut to length and powder coated?
Yes. Metline can cut to your list and supply mill finish, anodised or powder-coated box section, packed for export and shipped worldwide.
Need aluminium box section?
Send sizes, alloy, finish and quantities. We will reply with availability, cutting options and a delivered price.
