M10 Carriage Bolts A2-70 Stainless Steel | Round Head Square Neck Coach Screws

Generally, the bolt length should equal the total thickness of the materials being joined plus enough thread engagement for the nut — typically an additional 1–2× the bolt diameter. For M10 bolts, that means adding roughly 10–20mm beyond your material stack. For example, joining two 20mm boards would typically call for a 50mm (≈2") bolt. Always measure your full stack-up — including any washers — before selecting a length.

A2 refers to the austenitic stainless steel alloy group (equivalent to 304 stainless steel), and 70 indicates a minimum tensile strength of 700 MPa per ISO 3506. This makes them suitable for structural and load-bearing wood connections in most residential and light commercial applications, including decking, fencing, and timber framing.

A2 stainless steel offers excellent corrosion resistance and is generally suitable for outdoor, coastal, and humid environments — including rain-exposed decks, garden structures, and fence assemblies. For highly aggressive marine or chemical environments where saltwater immersion is frequent, A4 (316) stainless is typically recommended instead.

These are M10 metric coarse thread bolts conforming to ISO 8677 / DIN 603. They are compatible with standard M10 metric hex nuts and flat washers. They are not compatible with UNC or UNF inch-thread fasteners. If you are unsure of your existing hardware's thread standard, check the nut markings or measure the thread pitch before ordering.

The square neck is designed to embed into wood or soft materials as the nut is tightened, preventing the bolt from spinning in place. This allows single-person installation — you can drive the nut from one side without needing to hold the bolt head with a second wrench. It is particularly useful when the bolt head is recessed or in a hard-to-reach location.

Pack size varies by bolt length. Shorter bolts (40mm) are available in 15-piece packs, mid-range lengths (50mm–70mm) in 10-piece packs, and longer bolts (100mm) in 8-piece packs. For small repairs or prototyping, a single pack is typically sufficient. For larger builds such as full deck sections or fence runs, consider ordering multiple packs to reduce per-unit cost and avoid mid-project shortages.

A flat washer under the nut is generally recommended to distribute the clamping load across a wider surface area and protect the timber from the nut bearing directly into the grain. The domed round head on the bolt side typically does not require a washer, as it already provides a broad, smooth bearing surface. Washers are sold separately.