Short answer
HSS is hollow structural section (tube), written outside dimensions then wall thickness, like HSS6x6x1/4. L is an angle, written leg, leg, thickness. C and MC are channels, written depth then weight per foot. PL is a plate, written thickness then width.
Quick reference
| Designation | Shape | How to read it | Weight example |
|---|---|---|---|
| HSS6x6x1/4 | Square tube | 6 in x 6 in outside, 1/4 in nominal wall | 19.02 lb/ft |
| HSS4x4x3/8 | Square tube | 4 x 4, 3/8 wall | 17.27 lb/ft |
| L4x4x1/4 | Equal angle | Two 4 in legs, 1/4 in thick | 6.6 lb/ft |
| L3x3x1/4 | Equal angle | Two 3 in legs, 1/4 in thick | 4.9 lb/ft |
| C10x15.3 | American standard channel | 10 in deep, 15.3 lb/ft | 15.3 lb/ft |
| MC12x10.6 | Miscellaneous channel | 12 in deep, 10.6 lb/ft | 10.6 lb/ft |
| PL 1/2x12 | Plate | 1/2 in thick, 12 in wide | 20.4 lb per ft of length |
Each size above is in the shape database with full dimensions.
HSS: hollow structural sections
HSS covers square, rectangular and round tube. Rectangular reads as long side, short side, wall: HSS8x4x1/4. Round tube reads as outside diameter then wall. The weight comes from the table, and it is based on the design wall thickness, about 93 percent of nominal for the common ERW product. Do not compute weight from the nominal wall.
HSS is common for columns, braces and frames where the member shows. Pipe is a separate family (PIPE 4 STD, PIPE 6 XS), designated by nominal size and wall class, and is not the same as round HSS.
L: angles
Equal angles repeat the leg: L4x4x1/4. Unequal angles list the long leg first: L6x4x3/8. Back-to-back pairs show as 2L4x4x1/4 and double the weight. Angles are used for bracing, lintels, shelf angles and clips.
C and MC: channels
C is an American Standard channel and MC is a miscellaneous channel. Both read as depth then weight per foot. C channels are American Standard sections with standardized dimensions. MC channels are the other channels that do not follow the American Standard dimensions, and the family includes heavier sections. A C10x15.3 is 10 in deep and 15.3 lb/ft.
Channels frame stair stringers, edges of openings and platforms. See C vs MC channel sizes.
PL: plate
Plate reads thickness x width, with the length given separately or on a detail: PL 1/2x12x1'-0". Plate weight depends on area, about 40.8 lb per square foot for every inch of thickness. Base plates, gussets, stiffeners and connection plates are all PL.
Beware of plate callouts that are only a thickness and a note. A bare "PL 1/2" on a notes sheet is not a countable member. SteelFlo flags ambiguous plate callouts like that so you can confirm them instead of having them counted blindly.
Other designations you will meet
- S, M, HP, WT: see What does W10x15 mean?.
- PIPE: designated by nominal diameter and wall class (STD, XS, XXS). A PIPE 4 STD is not 4 inches outside; nominal pipe sizes do not equal the outside diameter.
- Round HSS: written outside diameter then wall, like HSS5.500x0.258, which weighs 14.46 lb/ft. It is different from pipe.
- FB or BAR: flat bar, written FB 3x1/4 for a 3 in x 1/4 in bar.
- RB or ROD: round bar, by diameter.
- JOIST (K, LH, DLH): open-web joists by series and depth, such as 16K5.
- Cold-formed: studs and tracks like 600S162-54, covered by SSMA designations.
If you meet a designation you do not recognize, check the drawing notes for a legend before guessing.
Common mistakes with these shapes
- Treating HSS wall thickness as the weight. HSS6x6x1/4 is not a 1/4 lb/ft member. It weighs 19.02 lb/ft.
- Using the nominal wall to compute weight. Use the table value, which is based on the design wall.
- Assuming L4x4x1/4 and L4x4x3/8 weigh the same because the legs match. Thickness changes the weight a lot.
- Mixing up C and MC. They are different families with different dimensions.
- Counting a plate callout on a note as a member. Plates need a size and a location.
- Forgetting that 2L means a pair and doubles the weight.
Look the size up. The database lists weight per foot for each one, so there is nothing to guess.
Which standards use which names?
The letters above are AISC (US). Other standards use different names for similar shapes: UB and UC in the UK, IPE and HE in Europe, UB, UC and PFC in Australia and New Zealand, and ISMB in India. A hollow section might be HSS in the US, SHS or RHS in the UK, Australia and Europe. See What is the UK equivalent of a W-beam? and How do Australian steel sections work?.
Look up the sizes
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