The wrong fastener in the wrong application will corrode, stain the timber, or fail structurally within a few years. The right one will outlast the structure. Here is how to read the options.
Zinc-plated: indoor and sheltered use only ¶
Zinc-plated fasteners are the standard option for most indoor applications. The zinc layer is thin (typically 5-8 microns on electroplated fasteners) and provides adequate corrosion resistance in dry, sheltered conditions. They are not suitable for outdoor use, contact with treated timber, or any application where they will be exposed to moisture regularly. The zinc layer will corrode within a few years in those conditions, leaving a rust stain on the timber and a weakened fastener.
Hot-dip galvanised: outdoor structural use ¶
Hot-dip galvanising applies a much thicker zinc layer (typically 45-85 microns) by dipping the fastener in molten zinc. This gives significantly better corrosion resistance than electroplated zinc. Hot-dip galvanised fasteners are the standard choice for outdoor structural applications: framing, decking, fencing, and pergolas. They are compatible with most treated timber. The surface is rougher than electroplated zinc, which can affect fit in pre-drilled holes.
A2 stainless (304 grade): general outdoor use ¶
A2 stainless steel contains 18% chromium and 8% nickel. It is resistant to most atmospheric corrosion and suitable for outdoor use in non-coastal environments. It is not suitable for contact with treated timber containing copper compounds (most modern ACQ and CA treated timber), because the copper accelerates corrosion of the stainless. For treated timber, use A4.
A4 stainless (316 grade): coastal and treated timber ¶
A4 stainless adds 2-3% molybdenum to the A2 composition, which significantly improves resistance to chloride corrosion. It is the correct choice for coastal sites, marine environments, and any application involving contact with treated timber. It costs more than A2 but the difference is worth it in any application where failure would require dismantling the structure to replace fasteners. We stock the full A4 range from M4 to M12 in socket cap, button head, and countersunk.
The fastener section of the catalog is organised by material and head type. If you are unsure which grade suits your application, email us the details and we will advise before you order.