HSS steel is hollow structural section: square, rectangular or round steel tube made to a structural standard and used for posts, columns, braces and frames. In Canada it is usually supplied to CSA G40.21 grade 350W or to ASTM A500, and it is described by outside size and wall thickness, for example HSS 102x102x6.4. If you came here from a machining search, HSS also means high-speed steel, a tool steel for drill bits and cutters, which has nothing to do with building structures.
This guide explains what structural HSS is, how it is made, how it differs from pipe and other tube, and where it makes sense. For sizes, grades, weights and prices we link to the detailed guides rather than repeat them.
HSS meaning: structural tube, not tool steel
The letters cause real confusion, so it is worth settling first.
| Term | What it means | Where you hear it |
|---|---|---|
| HSS (hollow structural section) | Steel tube made for load-bearing use, with guaranteed strength | Structural drawings, steel suppliers, fabricators |
| HSS (high-speed steel) | Hardened tool steel that keeps its edge when hot | Drill bits, saw blades, machining |
| Structural tubing | Everyday name for HSS | Contractors, homeowners |
| Pipe | Round tube made mainly for carrying fluids, ordered by nominal size and schedule | Plumbing, process piping, some posts and railings |
| Mechanical or decorative tube | Tube made for machinery, furniture or trim | Shops, retail metal stores |
On a Canadian structural drawing, "HSS" always means the first line. You will see it written as HSS followed by dimensions in millimetres, sometimes with the imperial name beside it (HSS 102x102x6.4 is the same tube as HSS 4x4x1/4). Our HSS size chart explains how those numbers are rounded from inch sizes and lists common sections with their mass per metre.
The three shapes
HSS comes in three families:
- Square HSS. Equal sides, the same strength about both axes. The default choice for posts and small columns, and common in frames, gates and railings because flat faces are easy to weld and bolt to.
- Rectangular HSS. One side longer than the other. Stiffer in the deep direction, so it works as a short beam, a lintel, a header, a stair stringer or a frame member that bends mainly one way. Sizes are written with the larger dimension first, such as HSS 152x102x6.4.
- Round HSS. Circular, sized by outside diameter and wall. Efficient as a column and in trusses and bracing, and it sheds wind and water well. Round HSS is harder to connect to than flat-sided tube, because plates and other members have to be shaped to the curve.
Each family comes in a range of wall thicknesses. A thicker wall adds strength and weight without changing the outside size, which is handy when a column needs more capacity but has to stay the same size as its neighbours.
How HSS is made
Most HSS in North America is made from flat steel strip. The strip is formed through a series of rolls into a round tube, the seam is welded, and the round is then squeezed through shaping rolls into a square or rectangle if needed. The result has a weld seam along one face (you can often spot it on the inside) and rounded corners rather than sharp ones.
That forming process matters for two reasons:
- Corner radius. The rounded corners mean square HSS is not a perfect box. It affects how plates sit at the corners and how fillet welds are sized at the edges.
- Class C and Class H. Under CSA G40.21, cold-formed tube left as formed is Class C. Tube that is stress-relieved or hot-formed is Class H, which has lower residual stresses and earns a higher column resistance in design. Our guide to HSS steel grades covers 350W, A500 and the Class C and Class H question in detail.
The grade and class are shown on the mill certificate. If your engineer specified one, check that the material supplied matches.
What HSS is used for
HSS turns up wherever a member carries load along its length, bends in more than one direction or is exposed to view.
In houses
- Basement posts and columns under steel or wood beams, with base and cap plates welded on. See HSS steel posts for basements and decks.
- Deck and porch posts, and posts for steel-framed decks and balconies.
- Short headers and lintels in some designs, usually rectangular sections.
- Stair stringers, railing posts and gate frames.
In commercial and industrial work
- Columns in steel-framed buildings, often square HSS with a W-shape beam framing in.
- Bracing in walls and roofs, where round or square HSS braces take tension and compression.
- Trusses, canopies, entrance frames and exposed architectural steel.
- Mezzanine columns, equipment supports and platforms.
In miscellaneous metal
- Railings and guards, gates and fences, sign structures, bollards and ladders.
HSS advantages and trade-offs
| Advantage | Why it helps |
|---|---|
| Strong about both axes | A square tube has no weak direction, which suits columns and posts |
| Resists twisting | The closed shape is far stiffer in torsion than an open W-shape or channel |
| Clean appearance | Flat or round faces with no flanges, so it looks tidy when exposed |
| Less surface to paint | No flange edges or inside corners to coat |
| Compact | A small HSS column can fit inside a wall or behind a finish |
| Trade-off | What to watch |
|---|---|
| Connections | You can't easily reach inside a closed tube to bolt it, so connections are usually welded plates, through-plates or special fasteners. Our post on HSS connections and framing details goes through the common ones. |
| Water inside | An open-ended tube outdoors can collect water, which rusts the inside and can split the tube if it freezes. Cap the ends or provide drain holes. |
| Weaker as a one-way beam | For a floor beam spanning one way, a W-shape usually gives more stiffness for the same weight |
| Inside corrosion | You can't paint the inside, so exterior tube is often sealed or galvanized |
For a direct side-by-side on real section properties, see our comparison of W-beams and HSS for beams and columns.
Steel tube calculator basics
People often search for a "steel tube calculator" when what they need is the weight of a length of HSS, to plan handling, delivery or a budget conversation. The quick method:
- Find the mass per metre for the exact section (size and wall) in a section table.
- Multiply by the length in metres.
- Add plates, caps and other fittings separately.
For example, HSS 102x102x6.4 is listed at 18.2 kg/m, so a 2.4 m post weighs about 44 kg before the base and cap plates. Our HSS weight per metre guide gives the full charts and the formulas for square, rectangular and round tube.
A weight calculator does not tell you whether a tube is strong enough. Column capacity depends on the length, the end conditions, the grade and class, and the loads, and that check belongs to a designer or engineer working to CSA S16. In houses, the Ontario Building Code also has its own rules for steel columns; our article on basement column rules in the Ontario Building Code explains them.
Ordering HSS: what to specify
When you order HSS, cut or fabricated, give the supplier:
- The full designation from the drawings, including wall thickness. "A 4 inch square tube" could be any of several walls with very different weights.
- The grade and class, if specified (for example 350W Class C), and whether you need mill certificates.
- Lengths and quantities, and whether ends are square cut or need plates.
- Plates and holes: base plates, cap plates, knife plates, slots and bolt holes.
- Finish: bare, primed, painted or another coating, and whether ends must be sealed.
- Delivery address and site access.
Getting HSS cut and fabricated
We supply HSS posts and frames cut to length or fabricated with base, cap and connection plates welded on, using CWB certified shop welding and in-house shop drawings, with delivery across the GTA and Ontario. If you have drawings, send them for a free take-off and quote. You can also see the steel posts and other sections we supply.
Frequently asked questions
What does HSS stand for in steel?
In construction, HSS stands for hollow structural section: a square, rectangular or round steel tube made for structural use. In machining, HSS means high-speed steel, a tool steel used for drill bits and cutters. The two are unrelated.
Is HSS the same as steel tubing?
HSS is structural steel tubing made to a structural standard, such as CSA G40.21 or ASTM A500, with known strength. Mechanical tubing and decorative tube look similar but are made to different standards and are not interchangeable in a structural design without an engineer's approval.
What is the difference between HSS and pipe?
Pipe is made mainly to carry fluids and is ordered by nominal pipe size and schedule. Round HSS is made for structural loads and is ordered by outside diameter and wall thickness to a structural grade. Some round sizes share the same outside diameter, but the standards and guaranteed properties differ.
What is HSS steel used for?
Columns and posts, braces, trusses, frames, canopies, railings, stairs, gates and equipment supports. The closed shape is strong in every direction and resists twisting, which suits members that carry axial load or bend both ways.
Is HSS stronger than an I-beam?
It depends on the job. For a column or a member that twists, HSS is often more efficient. For a floor beam bending one way, a wide-flange (W) shape of the same weight is usually stiffer. Your engineer chooses the section.
