Kumar IronUpdated
In this guide
The short answer
| Section | Typical use | Why |
|---|---|---|
| MS angle (ISA) | Truss members, window grills, gate frames, braces, shelf frames | Light, easy to cut and weld, good for bracing |
| MS channel (ISMC) | Purlins, frames, gate posts, base frames, staircase stringers | Flat back is easy to fix to, good in bending along one axis |
| MS beam (ISMB) | Columns, rafters, main girders, lintels over wide openings | Deep section, best for heavy bending loads |
MS angle: trusses, grills and gates
Angles are L shaped. Small sizes are used for window grills, gate frames and shelf racks. Medium sizes form the top and bottom chords and web members of light roof trusses on sheds. Because angles bend easily across the L, they are better as tension and bracing members than as main beams.
Sizes are written like 40 x 40 x 5 mm (leg, leg, thickness). Light jobs often use roughly 25 to 50 mm legs. Truss members and heavier frames often move to 50 to 100 mm legs. Treat these as guidance only. The structural engineer confirms sizing for load.
MS channel: purlins and frames
Channels (ISMC) are C shaped with a flat back, which makes it easy to bolt or weld other parts and to fix roof sheets. They are common as purlins across trusses, as frames for gates and doors, and as base frames for machines and water tanks.
Common sizes run from small channels like ISMC 75 up to ISMC 200 and above for heavy frames. Roof purlins on small sheds often use lighter sizes, while longer spans need deeper channels. The right size depends on span, spacing and roof load, and the engineer confirms sizing for load. See our purlin spacing guide for how purlins sit under sheets.
MS beam: columns, rafters and lintels
I beams (ISMB) have a deep web and two flanges, which resists bending very well. Use them for steel columns in sheds and godowns, for main rafters over larger spans and for lintels over wide openings such as shop fronts and garage doors in brick walls.
Sizes begin around ISMB 100 and go well above 300 for large spans. For a normal shop front or garage opening, a lintel beam must also bear properly on the wall each side, and the wall above adds load. Do not guess this one. The structural engineer confirms sizing for load, including bearing length.
Quick picks by project
- Gate: channel or hollow section frame with angle bracing. For pipe and hollow options see our MS pipe guide.
- Window grill: small angle or flat with square bars.
- Tin shed: beam or built up columns, angle trusses or beam rafters, channel purlins.
- Lintel over a door or window: RCC is usual, a steel beam suits wide shop openings or retrofits.
- Staircase: channel stringers with angle or flat supports.
Work out the weight before you order
Sections are sold by weight, so convert your length list to kilograms. Use our MS angle and channel weight chart and our ISMB I beam weight chart, then add some allowance for cutting waste and welding. Rates change daily, so call or WhatsApp the store for a quote on your sizes.
Frequently asked questions
- Can I use angle instead of channel for purlins?
- Angles are weaker in bending across one axis and can twist. Channels are the usual choice. The engineer decides based on span and load.
- What is the difference between ISMB and ISMC?
- ISMB is an I beam with two flanges and is deeper for its weight. ISMC is a channel with a flat back, easier to fix other parts to.
- Which section for a lintel over a shop front?
- Often an ISMB beam, but the size depends on span and wall load. Get it confirmed by a structural engineer.
- Where can I find the weight per metre?
- In our MS angle and channel weight chart and ISMB I beam weight chart.