A sign blank is a flat aluminium panel, cut to the finished shape of a sign, with rounded corners, deburred edges and mounting holes, ready for the sign maker to apply retroreflective sheeting or print. Road authorities typically call for 5052-H38 or 6061-T6 sheet to ASTM B209 at 0.080 in or 0.100 in, while 3003, 1100 and 5754 are used for lighter-duty and European signs. Metline supplies sign-grade sheet and cut-to-size blanks to sign fabricators worldwide.
Almost every permanent road, traffic, parking and facility sign is built on an aluminium substrate. The substrate, called a blank, is sheet that has been sheared or routed to shape, given radiused corners, deburred and, where needed, punched with mounting holes. The sign fabricator then cleans it, applies retroreflective sheeting or a printed film, and adds the legend.
Aluminium replaced steel and wood for signs because it does not rust, is about one third the weight of steel for the same volume, and holds a flat, smooth surface that sheeting adheres to for many years. A lighter panel also means lighter posts and brackets and makes breakaway and crash-safe sign supports easier to design.
The blank itself is a simple product, but small details decide how well the finished sign performs: the alloy and temper determine whether a large panel stays flat in wind, the surface treatment determines whether the sheeting stays bonded, and the edge and hole quality determine whether the sign can be handled and mounted safely. Metline supplies the aluminium sheet and the cut-to-size blanks; finished signs, sheeting and legends are produced by the sign maker.
The table compares the alloys most often specified. Typical tensile and yield strengths are Aluminum Association typical values for sheet; specified minimums under ASTM B209 or EN 485-2 are lower and are reported on the mill certificate.
| Alloy and temper | Typical tensile / yield | Where it is used | Notes |
|---|---|---|---|
| 5052-H38 | 290 / 255 MPa | Highway and street signs, especially 0.080 in panels | Stiff, strong, excellent corrosion resistance; the most widely specified sign alloy in North America |
| 6061-T6 | 310 / 276 MPa | Highway signs 0.100 in and thicker, large guide panels | Heat-treated strength; accepted as an alternative to 5052-H38 in many DOT specifications |
| 3003-H14 | 150 / 145 MPa | Parking, property, warning and informational signs | Lower cost, easy to form; less stiff, so used for smaller or thinner panels |
| 1100-H14 / 1050 | 125 / 115 MPa | Indoor, decorative and low-wind signs | Very formable and inexpensive; low strength |
| 5754-H22 / H24 | See EN 485-2 | European road signs and plates | Common European choice for durable sign panels with good corrosion resistance |
| 5454 | See ASTM B209 | Specialist signs in harsh environments | Similar corrosion behaviour to 5052 with slightly higher strength in some tempers |
The H38 temper of 5052 is strain-hardened and stabilised, which gives the stiffness and strength needed to keep a 30 or 36 in panel flat under wind load without a heavy gauge. 6061-T6 reaches similar strength by heat treatment. 3003 and 1100 are softer; they are perfectly adequate for parking and facility signs that are smaller, closer to the ground and often riveted to a frame.
A common specification in US state transportation departments reads: 5052-H38 for 0.080 in and thinner, and 6061-T6 or 5052-H38 for 0.100 in and thicker, all to ASTM B209. Always follow the wording of the contract you are supplying, because states and countries differ.
Shape carries meaning in road signing, and the blank must match the standard of the country where the sign will stand. In the US Manual on Uniform Traffic Control Devices (MUTCD) system, the octagon is reserved for STOP, the downward equilateral triangle for YIELD, the diamond for warnings, the pentagon for school zones, the circle for railway crossing advance warning, and rectangles for regulatory and guide signs. In the Vienna Convention system used across Europe, Asia and much of Africa, triangles warn, circles prohibit or instruct, and rectangles inform.
Weights of common square and rectangular blanks follow; they are calculated from 0.0975 lb/in³ and ignore holes and corner radii, which remove only a small fraction of the mass.
| Thickness | Size | Weight (lb) | Weight (kg) |
|---|---|---|---|
| 0.063 in (1.60 mm) | 12 × 18 in | 1.33 | 0.60 |
| 0.063 in (1.60 mm) | 18 × 24 in | 2.65 | 1.20 |
| 0.063 in (1.60 mm) | 24 × 24 in | 3.54 | 1.60 |
| 0.063 in (1.60 mm) | 24 × 30 in | 4.42 | 2.01 |
| 0.063 in (1.60 mm) | 30 × 30 in | 5.53 | 2.51 |
| 0.063 in (1.60 mm) | 36 × 36 in | 7.96 | 3.61 |
| 0.063 in (1.60 mm) | 48 × 48 in | 14.15 | 6.42 |
| 0.080 in (2.03 mm) | 12 × 18 in | 1.68 | 0.76 |
| 0.080 in (2.03 mm) | 18 × 24 in | 3.37 | 1.53 |
| 0.080 in (2.03 mm) | 24 × 24 in | 4.49 | 2.04 |
| 0.080 in (2.03 mm) | 24 × 30 in | 5.62 | 2.55 |
| 0.080 in (2.03 mm) | 30 × 30 in | 7.02 | 3.18 |
| 0.080 in (2.03 mm) | 36 × 36 in | 10.11 | 4.59 |
| 0.080 in (2.03 mm) | 48 × 48 in | 17.97 | 8.15 |
| 0.100 in (2.54 mm) | 12 × 18 in | 2.11 | 0.96 |
| 0.100 in (2.54 mm) | 18 × 24 in | 4.21 | 1.91 |
| 0.100 in (2.54 mm) | 24 × 24 in | 5.62 | 2.55 |
| 0.100 in (2.54 mm) | 24 × 30 in | 7.02 | 3.18 |
| 0.100 in (2.54 mm) | 30 × 30 in | 8.78 | 3.98 |
| 0.100 in (2.54 mm) | 36 × 36 in | 12.64 | 5.73 |
| 0.100 in (2.54 mm) | 48 × 48 in | 22.46 | 10.19 |
| 0.125 in (3.17 mm) | 12 × 18 in | 2.63 | 1.19 |
| 0.125 in (3.17 mm) | 18 × 24 in | 5.27 | 2.39 |
| 0.125 in (3.17 mm) | 24 × 24 in | 7.02 | 3.18 |
| 0.125 in (3.17 mm) | 24 × 30 in | 8.78 | 3.98 |
| 0.125 in (3.17 mm) | 30 × 30 in | 10.97 | 4.98 |
| 0.125 in (3.17 mm) | 36 × 36 in | 15.79 | 7.16 |
| 0.125 in (3.17 mm) | 48 × 48 in | 28.08 | 12.74 |
Retroreflective sheeting is bonded with a pressure-sensitive or heat-activated adhesive, and the bond is only as good as the aluminium surface underneath. Rolling oils, the natural oxide film and handling marks all reduce adhesion, so specifications require the blank to be degreased, etched and given a conversion coating before sheeting is applied.
The traditional treatment, often Class 2, which leaves a thin, adherent film ranging from iridescent silver to pale yellow. Many authorities still name it, but hexavalent chromium is being phased out for health and environmental reasons.
Trivalent or chromium-free coatings that meet the same adhesion and corrosion purposes. Several US states adopted ASTM B921 Class 1 in place of B449; check which one your contract calls for.
Some sign shops prefer mill-finish blanks and run their own cleaning and treatment line just before sheeting. In that case order clean, oil-free mill finish.
Anodising gives a durable, decorative finish for architectural and wayfinding signs where the metal itself is visible.
Polyester or PVDF painted coil, often white on the back, used for screen-printed or vinyl-applied signs. See colour-coated sheet.
Specifications sometimes require a degreased or painted back to resist corrosion and staining; state it on the order.
| Standard | Scope | Relevance to the blank |
|---|---|---|
| ASTM B209 | Aluminium and aluminium-alloy sheet and plate | Chemistry, temper, mechanical properties and thickness tolerance of the substrate |
| ASTM B449 / ASTM B921 | Chromate and non-chromate conversion coatings on aluminium | Pre-treatment before sheeting |
| ASTM D4956 | Retroreflective sheeting for traffic control | Sheeting types applied by the sign maker; affects how the blank must be prepared |
| MUTCD (US FHWA) | Shapes, sizes and colours of US traffic signs | Blank dimensions and corner radii follow the sign size tables |
| EN 12899-1 | Fixed vertical road traffic signs, Europe | Performance classes for plates, including deflection under wind load |
| IRC:67 (India) | Code of practice for road signs | Sign layout and materials for Indian roads |
In Europe, EN 12899-1 sets performance classes rather than prescribing an alloy: the plate must meet wind load and temporary deflection classes, and the manufacturer chooses thickness and stiffeners to achieve them. Large European sign plates are therefore often 2 – 3 mm sheet with extruded aluminium stiffening channels on the back.
Many US highway specifications use 0.080 in (about 2 mm) for signs up to around 9 sq ft and 0.100 in (about 2.5 mm) or 0.125 in for larger panels. Parking and property signs are often 0.063 or 0.040 in. In Europe, 2 – 3 mm is common, with stiffeners on large plates.
Both are accepted by most authorities. 5052-H38 has slightly better corrosion resistance and is the usual choice for 0.080 in blanks; 6061-T6 is slightly stronger and is common for 0.100 in and thicker panels. Use whichever your specification names.
The coating gives a clean, chemically stable surface that sheeting adhesive bonds to and that resists corrosion creeping under the sheeting. Without it, sheeting can lift at edges and holes. ASTM B449 (chromate) and ASTM B921 (non-chromate) are the usual references.
Yes. Blanks can be cut to any outline from a drawing, with your corner radius and hole sizes and positions, or supplied without holes for bracket or rivet mounting.
No. Metline supplies sign-grade aluminium sheet, coil and cut-to-size blanks. Sheeting, printing and legends are applied by the sign manufacturer.
Tell us the alloy, thickness, blank sizes and surface treatment. We will reply with availability and a delivered price for your location.
