Unistrut is not a C-channel in the structural sense. It is a brand of strut channel: a light, cold-formed steel channel about 41 mm (1-5/8 in) square, with in-turned lips and slotted holes, made to be assembled with spring nuts, bolts and fittings. A structural C-channel is a hot-rolled section such as a C150x12 or C200x17, several times thicker, designed for building loads and usually welded or bolted with plates. Strut is for supporting services and light equipment quickly and adjustably. Structural channel is for framing that carries real structural loads.
What strut channel is
"Unistrut" is the best-known brand name (it belongs to Atkore), but several manufacturers make the same kind of product, generally called strut or metal framing channel. The common features:
- Profile. The basic channel is 41 mm (1-5/8 in) wide and deep, with deeper and shallower versions and back-to-back combinations for heavier loads.
- Thickness. Commonly 12 gauge (about 2.7 mm) or 14 gauge (about 1.9 mm) steel.
- In-turned lips. The open face has lips that curl inward. Spring-loaded channel nuts slip in, twist and lock against the lips, so fittings can be attached anywhere along the length.
- Slots and holes. Many channels come with repeating slots in the back for bolting to surfaces.
- Finishes. Pre-galvanized, hot-dip galvanized, painted, stainless steel, aluminium and fibreglass versions are made for different environments.
- Standard. In North America, the Metal Framing Manufacturers Association publishes MFMA-4, the industry standard for metal framing channel and fittings.
Strut is sized and selected from the manufacturer's load tables, which give beam and column loads for each channel at given spans and connection conditions.
Structural C-channel, for comparison
A hot-rolled C-channel is rolled at a steel mill from billets or blooms. A C150x12, one of the lighter common sizes, is about 152 mm deep with a 5.1 mm web and flanges about 8.7 mm thick (average) and weighs about 12.2 kg/m. Standard channels run from C75 to C380; our C-channel size chart lists them all.
Structural channel is designed under CSA S16 and supplied to structural grades such as CSA G40.21 350W. It is cut, drilled, coped and welded to suit the drawings, and it connects with bolted or welded plates and clips.
Side by side
| Strut channel (Unistrut and similar) | Hot-rolled C-channel | |
|---|---|---|
| How it's made | Cold-formed from sheet | Hot-rolled at a mill |
| Typical size | 41 x 41 mm, with variants | 76 to 381 mm deep |
| Thickness | About 1.9 to 2.7 mm | Web about 3 to 18 mm, flanges about 7 mm and up |
| Connections | Channel nuts, bolts and fittings, no welding | Bolted or welded plates, clips and copes |
| Adjustability | High: fittings slide anywhere | Low: holes and welds are fixed |
| Load source | Manufacturer's load tables | Engineered design to CSA S16 |
| Typical use | Conduit, cable tray, pipe, ductwork, light racks | Framing, headers, stringers, ledgers, equipment supports |
| Installed by | Electricians, mechanical and service trades | Steel fabricators and erectors |
The thickness gap is the key. Most structural channels have webs two to several times thicker than heavy-gauge strut, and their depth gives them far more bending strength. Strut makes up for that with speed, adjustability and a large catalogue of fittings.
When strut is the right tool
Strut works best where loads are known and modest, and where the layout may change:
- Electrical and mechanical supports. Trapeze hangers for conduit, cable tray and piping, wall-mounted racks and panel supports.
- Light equipment frames. Small units, controls and instrument stands within the published load tables.
- Adjustable or temporary supports. Systems that may be reconfigured as a building's services change.
- Supports hung from structure. Strut is often hung from the building's beams with beam clamps or threaded rod, so the strut carries the services and the structural steel carries the strut.
In all of these, the anchors and the structure the strut hangs from must be able to take the load. That is a separate check from the strut itself.
When you need structural channel or a fabricated frame
Strut is the wrong choice when:
- The member carries building loads. Floors, roofs, walls, stairs, landings and mezzanines are structural framing designed by an engineer, built from hot-rolled shapes.
- Loads are heavy or concentrated. Hoists, large rooftop units, tanks, and anything that vibrates or swings usually need a designed steel frame. See our guide on sizing a beam for a hoist, gantry or monorail for how those loads are handled.
- Spans are long. Strut capacity drops quickly with span; a channel or W-shape keeps going.
- The support must be welded or rigid. Fabricated frames with welded joints don't rely on friction connections.
- Safety-critical loads. Anything where a failure could injure someone needs engineered design, whatever material is used.
A common and sensible arrangement is both together: a fabricated channel or beam frame carries the heavy load back to the building structure, and strut mounted on that frame carries the conduit and piping.
Corrosion and finishes
Both products rust if left bare, and the finish choice follows the environment:
- Strut is usually pre-galvanized for dry indoor use, with hot-dip galvanized, stainless, aluminium or fibreglass versions offered for damp, exterior or corrosive spaces. Cut ends on pre-galvanized strut lose their coating and are normally touched up.
- Structural channel is supplied bare, shop primed, painted or hot-dip galvanized after fabrication, as the specification requires.
When the two are combined, keep the protection consistent. Galvanized strut bolted to bare steel outdoors gives up its advantage at the connection, and stainless fittings on carbon steel need the designer's attention to avoid corrosion between dissimilar metals. Our guide to galvanized vs painted structural steel covers the structural side.
Strut post bases vs fabricated base plates
Searches for "base plate unistrut" usually come from people standing strut up as a post. Manufacturers sell post-base fittings for this, and they work within the loads in the catalogue for light stands and supports.
For posts that carry real loads, such as platform columns, equipment stands and canopy posts, the usual answer is a fabricated steel post, often HSS, with a welded base plate anchored to concrete. The plate size, thickness and anchor bolts come from the design. Our guide to steel post base plates and concrete connections explains how those are detailed, and HSS steel posts covers the post side.
Fabricated steel supports to your drawings
Strut and its fittings come from electrical and mechanical suppliers. When a support needs to be structural, we fabricate the channel, beam and post frames, base plates and brackets to your drawings in our CWB certified shop, then prime or galvanize to suit and deliver across the GTA and Ontario. Comparing other channel types? See C channel vs U channel and our guide to C-channel load capacity.
Send your drawings for a quote, or browse our steel products, including channels, beams, plates and posts.
Frequently asked questions
Is Unistrut the same as C-channel?
No. Unistrut is a brand of strut channel: a light, cold-formed 41 mm (1-5/8 in) channel with in-turned lips and slots, used with spring nuts and fittings to support conduit, pipe and equipment. A structural C-channel is a hot-rolled section, much thicker and stronger, used in building framing.
How thick is Unistrut?
Standard strut channel is commonly made in 12 gauge (about 2.7 mm) and 14 gauge (about 1.9 mm) steel, in a 41 mm square profile with deeper and shallower variants. Check the manufacturer's catalogue for the exact product.
Can Unistrut be used for structural support?
Strut is designed to carry the loads in its manufacturer's tables, typically services and light equipment. It is not a substitute for structural framing that carries floors, roofs or walls. Anything beyond published loads, or anything life-safety related, needs an engineer.
Can you weld Unistrut?
Strut systems are designed to be bolted, not welded. Welding burns off the zinc coating on galvanized strut and the thin steel distorts easily. If a support needs welded connections, a fabricated steel frame is usually the better answer.
