Stainless Steel Bolts & Fastners

This category stocks marine-grade stainless steel bolts, screws, nuts and fastenings for boat fittings, deck hardware and general repairs – sized and graded specifically for saltwater use, where a fastener in the wrong grade corrodes, stains or seizes within a single season afloat.

Grade matters more than it looks. A2 (304) stainless is fine for fittings that stay dry or see only occasional spray, but A4 (316) – sometimes labelled ‘marine grade’ – has added molybdenum that resists saltwater corrosion far better and is the right choice for anything permanently wet or below the waterline. Mixing metals causes galvanic corrosion, so match fastener grade to the fitting it’s going into, and avoid pairing stainless fixings directly against aluminium without an isolating washer.

For sizing, measure the existing bolt’s diameter and thread pitch rather than just its length, and where a fastener will be regularly removed (inspection hatches, service panels), a light marine anti-seize compound on the thread prevents galling.

Frequently asked questions

What’s the difference between A2 and A4 stainless?

A4 (316) contains molybdenum and resists saltwater corrosion significantly better than A2 (304), which is why A4 is the standard choice below the waterline or for permanently wet fittings.

Why has my stainless bolt started rusting?

Usually either the wrong grade for the exposure, or surface contamination from cutting/grinding standard steel nearby, which embeds particles that rust and stain the stainless.

How do I stop stainless bolts seizing on aluminium fittings?

Fit an isolating washer or use anti-seize compound on the thread – direct stainless-to-aluminium contact in saltwater causes galvanic corrosion that can weld the two together over time.