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Carriage Bolts
Carriage bolts provide a secure, anti-spin fixing solution for timber construction, available in a range of finishes to suit internal, external and corrosive environments.
About Carriage Bolts
Carriage bolts, also known as cup square bolts, are commonly used for clamping timber or attaching ironmongery to timber. They feature a smooth domed head and a square section beneath the head that locks into the timber during tightening, preventing the bolt from spinning.
This design allows secure tightening from one side and provides a neat, low-profile finish once installed. Carriage bolts are widely used in structural timber construction, landscaping, fencing, decking and general joinery applications.
Choosing the Right Bolt Size and Finish
| Consideration | What to look for |
|---|---|
| Load requirement | Choose a bolt size that safely supports the weight and forces involved. Structural applications will typically require larger diameters such as M10 or M12. |
| Materials being joined | Timber-to-timber, timber-to-steel or metal-to-metal connections may influence bolt size and the need for washers to spread the load. |
| Environment | Use zinc plated bolts for internal use, exterior-coated or galvanised bolts for outdoor applications, and stainless steel for damp, coastal or corrosive environments. |
| Nut and washer | Nuts and washers provide secure clamping, spread the load and help prevent loosening over time, especially on timber connections. |
| Corrosion resistance | Upgrade the finish where moisture, weather exposure or treated timber is present to ensure long-term performance. |
General rule: choose the smallest bolt size that safely meets the load requirement, and upgrade the finish where corrosion resistance is important.
Carriage Bolt Finishes and Applications
Carriage bolts are available in a range of finishes, each designed for specific environments and applications:
- Zinc Plated Carriage Bolts
Suitable for internal and sheltered applications where exposure to moisture is limited.
Commonly used for joinery, workshop assembly and general internal timber construction. - Hot Dipped Galvanised Carriage Bolts
Designed for external timber construction such as fencing, decking and landscaping.
The galvanised coating provides strong corrosion resistance for outdoor use. - Stainless Steel Carriage Bolts
Manufactured from A2 stainless steel for use in damp, coastal or corrosive environments.
Ideal for treated or green timber and applications where long-term durability is critical. - Exterior Green Carriage Bolts
Heavy-duty bolts with a multi-layer corrosion-resistant green coating, designed for
demanding external applications such as decking subframes, sleepers and landscaping structures. - Exterior Silver Carriage Bolts
Premium exterior fixings with a silver organic coating, offering extended corrosion
resistance for exposed outdoor timber construction.
Choosing the Right Bolt Size
| Bolt size | Typical uses | Load level |
|---|---|---|
| M6 | Brackets and fittings Light timber assemblies Small framing and fix-out work |
Light duty |
| M8 | Timber fencing and gates General construction and landscaping Timber-to-timber connections |
Medium duty |
| M10 | Decking subframes Structural timber connections Posts and beams |
Heavy duty |
| M12 | Structural timber construction Heavy fencing and landscaping Load-bearing timber connections |
Structural / load-bearing |
| M16 | Heavy timber construction Large posts and beams Structural and load-critical connections |
Heavy structural |
