Square Plate Washers Zinc BZP M8-M20 Box of 100

Square washers — sometimes called plate washers or square plate washers — do a simple job that round washers cannot always handle. By spreading the clamping load of a bolt or nut across a much larger surface area, they prevent the fastener from pulling through soft or fibrous materials like timber, OSB, and similar substrates. Where a standard round washer might bear on just a few square centimetres, a 50x50mm square washer gives the fastening a proper foothold. That is the whole point of them, and they do it reliably every time.

These are heavy duty BZP (Bright Zinc Plated) square washers, finished in Trivalent Chromium (Cr3) zinc plate. The Cr3 finish gives a clean, bright appearance and provides a solid level of corrosion resistance for general construction and joinery applications. They are not stainless steel, so for fully exposed outdoor or marine environments you would want to consider that, but for most building, carpentry, and structural joinery work they perform well.

Where Square Plate Washers Get Used

Square plate washers are a go-to component in timber frame construction, where bolt-through connections need load to be spread across the grain of the wood rather than concentrated at the bolt hole. Post and beam work, garden structures, pergolas, fencing, decking subframes, and internal structural joinery all use them regularly. They also appear in steel-to-timber connections, where the washer bridges across a wider surface than a standard round washer would cover.

The range here covers M8 through to M20 bolt diameters, with plate sizes of 40x40mm and 50x50mm depending on the size selected, and plate thicknesses of either 3mm or 5mm. The 5mm option on the M10 40×40 size is worth noting for applications where a bit more rigidity in the washer itself is useful — particularly where the surface is uneven or where you want to avoid any flex under load.

Selecting the Right Size

As a general guide, match the bolt diameter to the washer hole size and then choose the plate size based on the material you are bearing against. For most M10 and M12 timber bolting, the 50x50mm plate is a sensible default. For lighter M8 fixings, the 40x40mm plate is usually adequate. The M16 and M20 sizes with 50x50mm plates are more commonly used in structural or agricultural settings where larger fasteners are involved. Each box contains 100 washers, which makes these practical to buy by the box on any job where quantity is needed.

These square washers are a straightforward but essential component for anyone working with bolted timber connections. Buy the right size, torque them down properly, and they will not give you any trouble.