Wood screw Koelner/Rawlplug 8x320 mm washer head CS-8320 for timber connections

Koelner/Rawlplug wood screw CS-8320, size 8x320 mm with a washer (bearing) head, is designed for reliable timber connections and structural wood fastening. The long thread and substantial diameter provide strong withdrawal resistance and clamping force for joining beams, posts and heavy timber elements. The washer-style head increases bearing surface to distribute load and reduce localized crushing of soft or treated wood.

Advantages

This wood screw offers a combination of high pull-out strength and a wide bearing area thanks to its 8 mm diameter and washer head design. Its length ensures deep penetration for secure joins in thick members, while the washer head helps maintain compression and reduce splitting at the connection surface. The screw is suitable for use where mechanical fastening is preferred over nails or connectors, and it performs consistently when installed with correct pre-drilling and recommended tools.

Suitable for

• Joining beams, joists and posts in structural timber work
• Carpentry and joinery projects requiring strong mechanical fixings
• Decking, pergola and outdoor timber assemblies (when compatible with wood treatment)
• Repairing or reinforcing wooden frames and load-bearing connections

Key specifications

• Nominal diameter: 8 mm
• Length: 320 mm
• Head type: washer (bearing) head for increased contact area
• Thread: full/long thread suitable for deep timber penetration
• Material and finish: designed for structural use (confirm finish compatibility with treated wood)

How to use

Mark and clamp the timber elements to be joined, then drill an appropriate pilot hole to the recommended diameter and depth for the 8x320 mm screw to avoid splitting and to ease installation. Drive the screw with a suitable driver or impact tool, ensuring the washer head sits flush against the wood surface to provide even compression. For best results in structural applications, follow building regulations and use the correct spacing, edge distances and pre-drilling guidelines for the wood species and thickness involved.

Usage recommendations

Use corrosion-resistant fasteners and check compatibility of the screw finish with treated or preservative-treated timber for outdoor applications. When installing large-diameter screws in load-bearing connections, verify design loads and follow structural fastening practices, including pre-drilling, correct torque application and, where required, supplementary metal connectors or washers.