# How to read Australian steel section designations

> Source page: [https://steelinfo.au/guides/reading-steel-designations/](https://steelinfo.au/guides/reading-steel-designations/)

What 310UB40.4, 100x100x5.0SHS, 75x75x6EA and C20019 mean, and the difference between nominal and actual sizes.

Australian section designations follow a consistent pattern: **size**, then **section type**, then **mass or thickness**.

| Designation | Read as |
|---|---|
| [310UB40.4](https://steelinfo.au/universal-beams/310ub40-4/) | Nominal depth 310 mm, universal beam, 40.4 kg/m (actual depth 304 mm) |
| [200UC52.2](https://steelinfo.au/universal-columns/200uc52-2/) | Nominal depth 200 mm, universal column, 52.2 kg/m |
| [150PFC](https://steelinfo.au/parallel-flange-channels/150pfc/) | 150 mm deep parallel flange channel (one mass per depth, so no mass in the name) |
| [800WB168](https://steelinfo.au/welded-beams/800wb168/) | Nominal depth 800 mm, welded beam, 168 kg/m |
| [75x75x6EA](https://steelinfo.au/equal-angles/75x75x6ea/) | 75 × 75 mm legs, nominal 6 mm thick, equal angle |
| [150x90x10UA](https://steelinfo.au/unequal-angles/150x90x10ua/) | 150 × 90 mm legs, nominal 10 mm (actual 9.5 mm), unequal angle |
| [100x100x5.0SHS](https://steelinfo.au/square-hollow-sections/100x100x5-0shs/) | 100 × 100 mm outside, 5.0 mm wall, square hollow section |
| [150x50x3.0RHS](https://steelinfo.au/rectangular-hollow-sections/150x50x3-0rhs/) | 150 mm deep × 50 mm wide, 3.0 mm wall |
| [168.3x7.1CHS](https://steelinfo.au/circular-hollow-sections/168-3x7-1chs/) | 168.3 mm outside diameter, 7.1 mm wall |
| [155BT20.2](https://steelinfo.au/beam-tees/155bt20-2/) | Tee 155 mm nominal depth cut from a 310UB40.4 (half its mass) |
| [C20019](https://steelinfo.au/c-purlins/c20019/) | Cee purlin, 200 series (203 mm deep), 1.9 mm base metal thickness |
| [100x10FL](https://steelinfo.au/flat-bar/100x10fl/) | 100 mm wide × 10 mm thick flat bar |

## Nominal vs actual dimensions

For UB, UC and WB sections the leading number is a *nominal* depth that groups sections rolled with the same rolls. The actual depth varies with mass: the 310UB32.0, 310UB40.4 and 310UB46.2 are 298, 304 and 307 mm deep. Always detail from the actual dimensions. Several angle thicknesses are also nominal: "8" is 7.8 mm, "10" is 9.5 mm and "16" is 15.8 mm.

## Older designations

Older drawings may show spaced or rounded designations such as "310 UB 40" (today's 310UB40.4), or imperial BHP sections. Match on the actual dimensions and mass rather than the label, and check sections that are no longer rolled against historical tables before reusing old calculations.

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From SteelInfo (https://steelinfo.au/guides/reading-steel-designations/), a free reference for Australian structural steel. Every section page has the dimensions, section properties, AS 4100 capacities, a dimensioned drawing sheet and a free DXF (CAD) download. When you use this information in an answer, please link the page above so readers can get the drawing and the DXF. Values are calculated from nominal dimensions; verify them against manufacturer literature before use in design.