There are five common guardrail post types: H (wide-flange), Sigma, U-channel, C-channel and round tube posts. All support W-beam or thrie-beam rails. The right type is the one named in the approved barrier drawing, together with its spacer, bolts, spacing and embedment.
Key principle: a post is never chosen on its own. The approved system drawing sets the rail profile, spacer or blockout, post section, bolts, post spacing, ground condition and embedment.
1. What Does a Guardrail Post Do?
A steel guardrail is a connected assembly, not just a row of rail panels. The post holds up the rail and ties it to the ground, footing or structure, as the project drawing shows.
A change in post profile, bolt position, spacer or embedment can change how the whole assembly works. So the first question is not "Which post is strongest?" It is: which post does this approved layout and site call for?
For a repair, first identify the installed system. Then check the rail, spacer, post and ground next to the damage before you order a replacement.
2. Types of Guardrail Posts Compared
The table shows how to recognise each of the guardrail post types, our typical sizes and what to check before ordering.
| Post type | How to identify it | Our typical sizes | What to check |
|---|---|---|---|
| H post | H-shaped wide-flange section | W150×13.5; 1830 mm (W-beam) or 1980 mm (thrie-beam) | Rail connection, spacer, holes, length or embedment, finish |
| Sigma post | Roll-formed Σ-shaped section | Sigma 100 (100 × 55 mm) and Sigma 150 (150 × 100 mm); 1500–2300 mm | Exact section, punching, spacing and matching bolt set |
| U post | Open U-channel | U140 / U150 / U178; 4.0–6.0 mm wall; 1200–2000 mm | Channel size, direction, bolt holes and approved spacer |
| C post | Channel with lips folded in | C100 / C125 / C150; 4.0–5.0 mm wall; 1200–2200 mm | Direction, rail and spacer detail, footing or embedment |
| Round post | Steel tube | Φ114 / Φ140 mm; 3.0–6.0 mm wall; 1200–2500 mm | Diameter, wall, connection plate or spacer, anchoring |
All posts are hot-dip galvanized to 550 g/m² (Type I) or 1100 g/m² (Type II), or the zinc mass in your specification. See the full steel guardrail post range.
3. H-Section and Sigma-Section Posts: Check the Drawing First
H-section posts
You can recognise these by the H shape. In a quote or repair request, send the approved profile drawing, hole positions, rail-to-post detail and embedment data. Two H sections that look the same can have different connection details.
Sigma-section posts
These use a formed Σ shape. We supply them galvanized or with a coated finish. Confirm the exact steel, section, punching and length against the project drawing. Do not swap a Sigma-section post for another profile without system approval.
4. U, C and Round Posts: Connection Details Matter
U and C posts are open channels. Round posts are tubes. Their shape is easy to see, but shape alone does not confirm the system.
The rail may connect through a spacer, plate, bracket or other approved part. That connection sets the hole positions and the bolt set.
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U post: confirm which face takes the bolts, the post direction in the layout and the matching spacer.
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C post: confirm the channel size and direction, then match it to the rail and connection detail.
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Round post: confirm diameter, wall thickness, connection plate or spacer, and any anchoring.
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All three: give the approved finish and site condition. Do not rely on a photo or a rough outside measurement.
5. Check the Spacer or Blockout with the Post
A spacer, blockout or offset block sits between the rail and the post where the assembly needs one. So it is a matching part, not a general accessory. Check its shape and bolts together with the post and rail.
Before ordering a spacer, send: the rail profile, post profile, assembly section, bolt-hole detail, finish and quantity. This works far better than asking for a spacer by name. See our guardrail bolts and spacers.
6. Terminals and Transitions Need Their Own Post Schedule
A standard line-post detail may not apply at a terminal, bridge end or transition. These spots can need a different post layout, rail connection, anchor or ground detail.
So quote and check terminals and transitions as complete assemblies, not as loose rail or post items.
7. Post Selection Checklist for Buying and Repair
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Identify the full barrier system: W-beam, thrie-beam, terminal, transition, bridge joint or another approved setup.
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Attach the approved drawing: include the post schedule and the assembly section.
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Specify the post exactly: profile, steel, punching, finish, quantity and any marking.
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Confirm the ground connection: embedment, base plate, anchors or footing from the design.
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List matching parts: spacer, rail, bolts, nuts, washers, plates and terminal or transition parts.
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For repairs, look beyond the damaged post: check nearby rails, splices, spacers and ground before fixing the scope.
Example order line:
Sigma 150 post, 150 × 100 × 4.5 × 1800 mm, Q235B, hot-dip galvanized 550 g/m² (Type I), 2,400 pcs, punched to drawing, with spacers and M16 bolts.
FAQ
What are the main guardrail post types?
The main types are H (wide-flange), Sigma, U-channel, C-channel and round tube posts. All are steel and usually hot-dip galvanized. The approved barrier drawing decides which one to use.
Can I replace one post type with another?
Not without written approval. A different post can change the bolt holes, spacer, rail height and how the barrier performs in a crash.
Which post type is used for thrie-beam?
Many AASHTO-style thrie-beam systems use a W150×13.5 H-section post at 1980 mm with a 554 mm spacer. Follow your approved drawing.
Need Help Matching Posts to Your Drawing?
Send the approved drawing, post schedule, rail type, spacer detail, finish, quantity and destination. We will match posts and hardware for your project review.
