M12 x 100mm coach bolt set — zinc plated bolt, nut and washer. Heavy-duty M12 for timber purlin connections where higher shear capacity is needed.
What Are Coach Bolts?
Coach bolts (also called carriage bolts) are designed for fixing timber to steel. They have a domed head with a square neck underneath that pulls into the timber as you tighten the nut, stopping the bolt from spinning. This means you only need a spanner on the nut side — no need to hold the bolt head.
In portal frame construction, coach bolts are used to fix timber purlins and side rails to the steel purlin cleats. The bolt passes through the timber purlin, through the cleat, and is secured with a nut and washer on the back. They’re also used for fixing timber cladding rails, gable framing, and any other timber-to-steel connection on the building.
Which Size Do I Need?
Coach bolt size is specified on your connection details, but the general rule is: the bolt needs to be long enough to pass through the timber, through the cleat, and have enough thread sticking out for the nut and washer.
Common sizes for portal frame buildings:
- M8 — lighter timber connections, battens, secondary framing
- M10 — standard timber purlin connections to steel cleats (most common for agricultural buildings)
- M12 — heavier timber purlins, double-bolted connections, or where higher shear loads apply
- M16 — heavy-duty timber connections, large section purlins
For bolt length, measure your timber thickness plus the cleat thickness plus 25-30mm for the nut and washer. For example, a 47mm timber purlin on a 6mm cleat needs roughly 80mm minimum bolt length.
How Many Coach Bolts Per Building?
Every purlin cleat needs coach bolts, typically 2 per cleat. A typical 6-bay agricultural shed with 7 frames might have 6 purlins per roof slope (12 total across both slopes) plus 6-8 side rails.
Each purlin is bolted at every frame position, so that’s 7 cleats × 2 bolts = 14 coach bolts per purlin run. For the purlins alone that’s around 168 coach bolts, plus another 80-100 for side rails — so budget for roughly 200-250 coach bolts for a typical 6-bay shed.
Always count from your drawings for an accurate number.
What Else Do I Need?
Coach bolt sets include the bolt, nut, and washer. For a complete purlin fixing you’ll also need the purlin cleats themselves — we sell both single and double timber purlin cleats.
Why Buy Coach Bolts From Us?
- Sold individually — order the exact quantity you need, no box quantities
- Complete set — bolt, nut, and washer included
- Zinc plated — corrosion resistant for external use
- Full size range — M6 to M16, lengths from 30mm to 200mm
Not sure which size you need? Send us your purlin detail drawing on WhatsApp and we’ll confirm the right coach bolt for your build.
Delivery Information
Next-Day Dispatch
Orders placed before 12pm (Mon–Fri) are dispatched the same day for next working day delivery (subject to courier availability).
Standard Delivery Cost
Shipping is calculated at checkout based on weight. Depending on weight or order we will send components in boxes or pallet delivery.
Packaging
All components are securely pallet-wrapped and labelled, ensuring safe and tidy arrival on-site.
Order Tracking
You’ll receive an email with tracking info once your order leaves our workshop.
Returns
We supply components made to spec, if you’ve ordered the wrong item or something’s arrived damaged, just let us know within 5 working days and we’ll sort it.
For full details, see our Returns Policy.
