Penny / Mudguard Washers M3–M10 — A4 Marine 316 DIN 9021

Why choose these A4 316 Penny / Mudguard Washers

Pressed from A4 (AISI 316) marine grade stainless steel to DIN 9021 — the European standard for large-OD flat washers, also known as penny washers, repair washers or mudguard washers. The oversized outside diameter spreads bolt load over a much wider area than a standard form A washer, making them ideal for soft timber, plastic, sheet metal and worn or oversized clearance holes.

A4 contains added molybdenum, which resists the chlorides that cause pitting corrosion in salt water, salt-laden air and de-icing salt. If the fixing lives indoors or well away from salt, our A2 stainless penny washers do the same job for less — see our guide to choosing between A2 and A4.

Sizes available

Each washer is specified by bolt size × outside diameter:

• M3 — 9mm or 12mm OD
• M4 — 12mm, 16mm, 20mm or 25mm OD
• M5 — 15mm, 20mm or 25mm OD
• M6 — 18mm, 24mm or 30mm OD
• M7 — 22mm OD
• M8 — 24mm or 32mm OD
• M10 — 25mm, 30mm or 40mm OD

Large sizes, sold by the box

M12 to M30 are available in full manufacturer's boxes. DIN 9021 standard OD: M12 × 37mm, M14 × 44mm, M16 × 50mm, M18 × 56mm, M20 × 60mm, M24 × 72mm and M30 × 92mm. A wider-OD pattern is also available in M12 × 48mm, M14 × 56mm and M16 × 64mm.

Please note: box quantities are ordered in to your requirement rather than held on the shelf — allow up to 2 weeks for delivery. Every pack of 10 or 20 is in stock for same-day dispatch as usual.

Pack options

M3–M10 are available in packs of 10 or 20. M12–M30 are supplied by the box (25, 50, 100 or 200 pieces depending on size).

Typical uses

• Boat and yacht fittings, deck hardware and chandlery
• Coastal balustrades, handrails and external ironmongery
• Poolside and spa hardware, where chlorine attacks lesser grades
• Trailers, horseboxes and anything exposed to gritted winter roads

How to fit

Place the washer between the work surface and the bolt head (or under the nut) before tightening, with the bolt sitting centrally in the clearance hole. Pair with A4 bolts and nuts — mixing grades in a wet joint invites galvanic corrosion and undoes the benefit of paying for A4.

Delivery

Same-day dispatch on orders placed before 2pm, Monday to Friday, on all pack sizes of 10 and 20. Box quantities allow up to 2 weeks. Free UK delivery on orders over £20.