M10 Carriage Bolts A2 Stainless Steel — Cup Square Dome Head Coach Screws DIN 603

A general rule is to add the total thickness of all materials being joined, then add at least 1–1.5× the bolt diameter (10mm) to account for the nut and washer stack. For example, joining two 25mm (1") boards typically calls for a 60mm (≈2-3/8") bolt. Always measure your actual grip length before selecting a size. If you're between sizes, go longer — you can always add a washer to take up slack.

These bolts are made from A2 stainless steel (equivalent to 304 stainless). Compared to standard zinc-plated or hot-dip galvanized carriage bolts, A2 stainless offers superior long-term corrosion resistance without the white rust or coating degradation common with zinc finishes — particularly in humid, coastal, or outdoor environments. For highly aggressive saltwater or chemical exposure, A4 (316) stainless is generally the better choice.

Yes. A2 stainless steel provides solid resistance to rust and oxidation, making these bolts well-suited for outdoor decking, fencing, pergolas, garden structures, and similar applications. They are not recommended for continuous saltwater immersion or highly corrosive chemical environments — for those conditions, A4 (316) stainless is typically the better specification.

These carriage bolts conform to DIN 603 and use the standard M10 metric coarse thread (pitch 1.5mm). They are compatible with any standard M10 hex nut, nylon insert lock nut (Nyloc), or flange nut. A flat M10 washer under the nut is recommended to distribute clamping load and protect the wood surface.

The square section of the shank, located directly beneath the dome head, is designed to bite into the wood fiber as the nut is tightened. This self-locking action holds the bolt stationary so you can apply torque from the nut side only — no need to hold the head with a second tool. This makes them especially practical when the bolt head is recessed or on the underside of a structure.

In most cases, a flat washer is placed under the nut (not under the dome head). The dome head is designed to seat directly against the workpiece surface. The washer on the nut side distributes the clamping force over a larger area, reducing the risk of the nut pulling through softer wood. For hardwoods or steel-to-wood connections, a washer may not be strictly necessary but is still good practice.

A2 stainless steel fasteners typically carry a tensile strength of around 500–700 MPa, depending on the property class (A2-50 or A2-70). For structural or load-bearing applications — such as deck ledger connections or load-path timber joints — always confirm the required load rating with a licensed engineer and consult local building codes before specifying fastener size and quantity.