Aluminium square bar is solid bar with four equal flat sides, extruded or cold-drawn in grades such as 6061, 6063, 6082, 7075, 2024 and 5083 and sold from about 3 mm to 250 mm across flats. Square hollow bar is the same outline with a bore, for lighter frames and parts. This guide compares grades and tempers, gives weights and section properties, explains tolerances and standards, and lists what to include in an order.
Square bar is one of the basic mill shapes, alongside round, flat and hexagonal bar. Its flat faces make it easy to clamp, mark out and machine, and its symmetric section has the same stiffness about both axes, so it is a natural choice for frames, guides, spacers, keys, fixtures and any part that will be milled to a rectangular shape.
Two product families share the name. Solid square bar is fully dense, and is chosen when parts are machined from it or when maximum strength and stiffness per outline are needed. Square hollow bar (often called square tube when the wall is thin) has a central bore; it saves weight and material in structures where load is carried mainly by the outer fibres, such as frames, posts and handrails.
Grade selection follows the same logic as for other bar forms. 6061 and 6082 are general structural grades; 6063 is chosen for its surface finish; 7075 and 2024 are high-strength aerospace and tooling grades; 5083 is used where seawater resistance matters; and free-machining 2011 is used for turned and milled parts made in volume.
A heated billet is pushed through a square die. This is the main route for sizes from about 10 mm to over 200 mm. Corners can be sharp or radiused, and the bar is stretched after quenching (T6511) to straighten it and relieve stress. Tolerances follow EN 755-4 or ASTM B221 tables.
Extruded bar drawn through a die at room temperature. Gives tighter dimensions, sharper corners and a brighter surface, and is common from about 3 mm to 100 mm. Covered by EN 754-4 and ASTM B211.
Large squares beyond the extrusion range, or squares in stress-relieved T651 plate tempers, are sawn from thick plate. Useful for one-off blocks and very large sizes.
Produced through porthole (bridge) dies in 6063, 6061 and 6082, giving seam-welded-in-the-die tube with consistent wall. Seamless hollow bar is extruded over a mandrel for high-strength or pressure uses.
Hollow extrusions drawn to final size for precise outer dimensions and walls, for example 2024-T3 drawn square tube to aerospace specifications.
For very large sections or where grain flow and through-thickness properties matter, squares can be open-die forged and machined.
Registered Aluminum Association limits (also used by EN 573-3). Single values are maxima; aluminium is the remainder.
| Grade | Si | Fe | Cu | Mn | Mg | Cr | Zn | Ti |
|---|---|---|---|---|---|---|---|---|
| 6061 | 0.40 – 0.8 | 0.7 | 0.15 – 0.40 | 0.15 | 0.8 – 1.2 | 0.04 – 0.35 | 0.25 | 0.15 |
| 6063 | 0.20 – 0.6 | 0.35 | 0.10 | 0.10 | 0.45 – 0.9 | 0.10 | 0.10 | 0.10 |
| 6082 | 0.7 – 1.3 | 0.50 | 0.10 | 0.40 – 1.0 | 0.6 – 1.2 | 0.25 | 0.20 | 0.10 |
| 7075 | 0.40 | 0.50 | 1.2 – 2.0 | 0.30 | 2.1 – 2.9 | 0.18 – 0.28 | 5.1 – 6.1 | 0.20 |
| 2024 | 0.50 | 0.50 | 3.8 – 4.9 | 0.30 – 0.9 | 1.2 – 1.8 | 0.10 | 0.25 | 0.15 |
| 5083 | 0.40 | 0.40 | 0.10 | 0.40 – 1.0 | 4.0 – 4.9 | 0.05 – 0.25 | 0.25 | 0.15 |
Typical values (ASM / Aluminum Association data) show how the grades compare. For design, use the specified minimums of the order standard, which fall with increasing section size for the heat-treatable grades and are reported on the mill certificate.
| Grade & temper | Tensile (MPa) | Yield 0.2 % (MPa) | Elongation (%) | Hardness (HB) |
|---|---|---|---|---|
| 6061-T6 / T6511 | 310 | 276 | 12 | 95 |
| 6063-T5 | 186 | 145 | 12 | 60 |
| 6063-T6 | 241 | 214 | 12 | 73 |
| 6082-T6 (EN 755-2 min., 20 – 150 mm) | 310 | 260 | 8 | — |
| 7075-T6 / T6511 | 572 | 503 | 11 | 150 |
| 2024-T351 | 469 | 324 | 19 | 120 |
| 5083-H112 (EN 755-2 min.) | 270 | 110 | 12 | — |
| 2011-T3 (free-machining) | 379 | 296 | 15 | 95 |
Because the modulus is nearly the same for all grades, choosing a stronger alloy raises the load a square bar can carry before yielding, but not its deflection under a given load.
| Temper | Meaning | When to order it |
|---|---|---|
| T6 | Solution heat-treated and artificially aged | Cold-finished bar and light machining |
| T6511 | T6, stretched to relieve stress, with minor straightening allowed | Extruded bar that will be heavily machined; stays straight and flat |
| T651 | T6 stress-relieved by stretching (rolled or cold-finished bar, plate) | Large squares cut from plate, precision parts |
| T5 | Cooled from extrusion and artificially aged | 6063 and 6060 architectural and decorative bar |
| T3 / T351 / T3511 | Solution treated, cold worked, naturally aged (stress-relieved variants) | 2024 aerospace parts and fittings |
| H112 | As fabricated with some control of properties | 5083 and other non-heat-treatable bar |
| O | Annealed, softest | Bending or forming before heat treatment |
Quote the standard on your drawing and the bar will be supplied and certified to it. The most common are:
| Standard | Scope | Typical use |
|---|---|---|
| ASTM B221 / ASME SB221 | Extruded bars, rods, wire, profiles and tubes | Extruded square bar, North America and global projects |
| ASTM B211 / ASME SB211 | Rolled or cold-finished bar, rod and wire | Cold-finished square bar |
| AMS-QQ-A-200/8, /11, /3 | Extruded 6061, 7075 and 2024 bar and shapes | Aerospace extruded square bar |
| AMS-QQ-A-225/8, /9, /6 | Rolled or drawn 6061, 7075 and 2024 bar | Aerospace cold-finished bar |
| EN 755-2 / EN 755-4 | Extruded bar mechanical properties / square bar tolerances (10 – 220 mm) | European extruded square bar |
| EN 754-2 / EN 754-4 | Cold-drawn bar properties / square bar tolerances (3 – 100 mm) | European drawn square bar |
| JIS H4040 · GB/T 3191 · IS 733 | National bar and rod standards | Japanese, Chinese and Indian projects |
Specifications such as ASTM B316 (rivet and cold-heading wire and rod) do not apply to square bar; check that the standard on an order actually covers the product form.
Weight of solid square bar (density 2.70 g/cm³): kg/m = side (mm)² × 0.0027. For 7075 multiply by 1.04 and for 5083 by 0.98. Second moment of area I = a⁴/12 and section modulus Z = a³/6 about either axis.
| Side (mm) | kg per metre | kg per 3 m bar | I (cm⁴) | Z (cm³) |
|---|---|---|---|---|
| 6 | 0.097 | 0.29 | 0.0108 | 0.036 |
| 8 | 0.173 | 0.52 | 0.0341 | 0.0853 |
| 10 | 0.270 | 0.81 | 0.0833 | 0.167 |
| 12 | 0.389 | 1.17 | 0.173 | 0.288 |
| 15 | 0.608 | 1.82 | 0.422 | 0.562 |
| 16 | 0.691 | 2.07 | 0.546 | 0.683 |
| 20 | 1.080 | 3.24 | 1.33 | 1.33 |
| 25 | 1.688 | 5.06 | 3.26 | 2.6 |
| 30 | 2.430 | 7.29 | 6.75 | 4.5 |
| 35 | 3.308 | 9.92 | 12.5 | 7.15 |
| 40 | 4.320 | 12.96 | 21.3 | 10.7 |
| 45 | 5.468 | 16.40 | 34.2 | 15.2 |
| 50 | 6.750 | 20.25 | 52.1 | 20.8 |
| 60 | 9.720 | 29.16 | 108 | 36 |
| 70 | 13.230 | 39.69 | 200 | 57.2 |
| 80 | 17.280 | 51.84 | 341 | 85.3 |
| 90 | 21.870 | 65.61 | 547 | 122 |
| 100 | 27.000 | 81.00 | 833 | 167 |
| 120 | 38.880 | 116.64 | 1.73e+03 | 288 |
| 150 | 60.750 | 182.25 | 4.22e+03 | 562 |
| 200 | 108.000 | 324.00 | 1.33e+04 | 1.33e+03 |
| 250 | 168.750 | 506.25 | 3.26e+04 | 2.6e+03 |
Imperial sizes are common in the Americas, usually in 12 ft (3.66 m) lengths. Weight in lb/ft = side (in)² × 1.17 for 6061.
| Size (in) | Size (mm) | lb per foot | kg per metre |
|---|---|---|---|
| 1/4 | 6.3 | 0.073 | 0.109 |
| 3/8 | 9.5 | 0.165 | 0.245 |
| 1/2 | 12.7 | 0.292 | 0.435 |
| 5/8 | 15.9 | 0.457 | 0.680 |
| 3/4 | 19.0 | 0.658 | 0.980 |
| 1 | 25.4 | 1.170 | 1.742 |
| 1-1/4 | 31.8 | 1.828 | 2.722 |
| 1-1/2 | 38.1 | 2.632 | 3.919 |
| 2 | 50.8 | 4.680 | 6.968 |
| 2-1/2 | 63.5 | 7.312 | 10.887 |
| 3 | 76.2 | 10.530 | 15.677 |
| 4 | 101.6 | 18.720 | 27.871 |
| 5 | 127.0 | 29.250 | 43.548 |
| 6 | 152.4 | 42.120 | 62.710 |
For a square hollow section of outside side B and wall t (both mm), area = B² − (B − 2t)² and kg/m = [B² − (B − 2t)²] × 0.0027. Corner radii reduce the true weight slightly; the figures below assume sharp corners.
| Outside (mm) | Wall (mm) | Area (mm²) | kg per metre | Weight saving vs solid |
|---|---|---|---|---|
| 10 × 10 | 1 | 36 | 0.097 | 64 % |
| 15 × 15 | 1.5 | 81 | 0.219 | 64 % |
| 20 × 20 | 1.5 | 111 | 0.300 | 72 % |
| 20 × 20 | 2 | 144 | 0.389 | 64 % |
| 25 × 25 | 2 | 184 | 0.497 | 71 % |
| 30 × 30 | 2 | 224 | 0.605 | 75 % |
| 30 × 30 | 3 | 324 | 0.875 | 64 % |
| 40 × 40 | 2 | 304 | 0.821 | 81 % |
| 40 × 40 | 3 | 444 | 1.199 | 72 % |
| 50 × 50 | 3 | 564 | 1.523 | 77 % |
| 50 × 50 | 5 | 900 | 2.430 | 64 % |
| 60 × 60 | 4 | 896 | 2.419 | 75 % |
| 80 × 80 | 4 | 1216 | 3.283 | 81 % |
| 100 × 100 | 5 | 1900 | 5.130 | 81 % |
| 120 × 120 | 6 | 2736 | 7.387 | 81 % |
| 150 × 150 | 10 | 5600 | 15.120 | 75 % |
| 200 × 200 | 10 | 7600 | 20.520 | 81 % |
6063-T5 and T6 dominate thin-wall hollow bar for frames, furniture and architectural work because they extrude easily and anodise well. 6061-T6 and 6082-T6 are used for structural hollow sections, while drawn 2024-T3 square tube to aerospace specifications covers small, high-strength sizes.
Tolerance standards define the permitted variation in width across flats, corner radius, straightness, twist, squareness of the faces and of cut ends. Extruded bar has wider limits than cold-finished bar, and the softer 6060/6063 group is held tighter than hard alloys such as 2024 and 7075, which are more difficult to extrude.
2011, 7075 and 2024 machine best, giving small chips and fine finishes. 6061 and 6082 in T6 machine well with sharp, high-rake carbide tooling. 6063 and 5083 are softer and can be gummy; use polished flutes and plenty of coolant.
6061, 6063, 6082 and 5083 weld readily by MIG and TIG. The heat-affected zone of T6 bar loses part of its strength, so welded frames are designed to reduced stresses. 7075 and 2024 are not recommended for fusion welding.
Small squares bend in O or T4 temper; T6 square bar needs generous radii. Square hollow bar can buckle on the inside of a bend, so use formers or filler material.
6063 gives the most uniform decorative anodised finish; 6061 and 6082 anodise well; 2024 and 7075 suit hard anodising but colour less evenly.
5083 and 6xxx grades resist atmospheric and marine exposure well. 2024 and 7075 need anodising, primer or cladding in corrosive environments.
Bars can be supplied sawn to length, squared and deburred, or machined to drawing.
| Sector | Solid square bar | Square hollow bar |
|---|---|---|
| Machinery and automation | Guides, keys, spacers, fixture blocks, gibs | Light frames, guards, gantries |
| Construction and architecture | Balusters, support bars, trim | Posts, mullion cores, handrails, frames |
| Transport | Brackets, mounting blocks, seat parts | Vehicle frames, racks, trailer components |
| Aerospace | 2024 and 7075 fittings and machined parts | Drawn 2024 square tube for structures |
| Marine | 5083 and 6082 deck fittings and cleats | Rails, frames, gangways |
| Tooling and moulds | 7075 and 6061 blocks for jigs and moulds | — |
| Furniture and displays | Decorative trim, legs | Furniture frames, shelving, display stands |
| Property | 6061-T6 | 6063-T6 | 6082-T6 | 7075-T6 | 2024-T351 | 5083-H112 |
|---|---|---|---|---|---|---|
| Strength | Medium-high | Medium | Medium-high | Very high | High | Medium |
| Machinability | Good | Fair | Good | Excellent | Very good | Fair |
| Weldability | Good | Very good | Good | Poor | Poor | Excellent |
| Corrosion resistance | Good | Very good | Good | Fair | Fair | Excellent |
| Anodised appearance | Good | Excellent | Good | Fair | Fair | Fair |
| Relative cost | Low | Lowest | Low | High | High | Medium |
A common mistake is specifying 7075 for a part that is stiffness-limited rather than strength-limited. Since all grades have nearly the same modulus, a stiff 6061 bar of a larger size often does the job at lower cost. Another is ordering T6 rather than T6511 for extruded bar that will be milled heavily on one side: the unrelieved bar can bow as stress is released.
Square bar is priced on weight. The metal cost follows the LME aluminium price plus the regional premium; the conversion cost covers billet casting, extrusion or drawing, heat treatment, stretching and inspection. On top come cutting, packing, freight and duties to your destination.
Multiply the side in millimetres by itself and by 0.0027 to get kg per metre. A 25 mm square bar weighs about 1.69 kg/m, and a 50 mm bar about 6.75 kg/m.
2011-T3 machines best of all, followed by 7075 and 2024. For a general-purpose bar that also welds and anodises, 6061-T6511 or 6082-T6 is the usual choice.
Both have the same strength. T6511 extruded bar has been stretched to relieve quench stresses, so it stays straight when machined; T6 is common for cold-finished bar.
Largely yes. "Hollow bar" is often used for heavier walls and small bores, "tube" for thinner walls, but both describe a square outline with a bore.
Cold-drawn bar from about 3 mm, extruded bar from about 10 mm to over 200 mm across flats, and larger squares cut from plate. Imperial sizes from 1/4 in to 6 in and beyond are also supplied.
Yes. Bars can be saw-cut to length, deburred and supplied with mill certificates, and machined to drawing on request.
Send grade, temper, size, length and quantity. We will reply with availability, tolerances, certification and a delivered price.
