A2 304 Stainless Steel Carriage Bolts — Cup Square Dome Coach Screws M6 M8 M10 M12

As a general rule, the bolt length should equal the total thickness of the materials being joined plus enough thread engagement for the nut — typically at least 1× the bolt diameter. For example, joining two 20mm (≈3/4") boards with an M8 bolt would generally require a bolt of at least 50mm (≈2"). When in doubt, size up by one increment. Lengths in this listing run from 12mm (≈1/2") to 100mm (≈3-15/16").

A2 304 stainless steel carriage bolts are typically rated to property class 70 per ISO 3506, with a tensile strength of generally around 500–700 MPa (≈72,000–101,000 psi) depending on diameter. For structural or load-bearing applications, always verify specific load requirements with a qualified engineer.

Yes — A2 304 stainless steel provides excellent corrosion resistance for most outdoor applications including decking, fencing, pergolas, and garden structures exposed to rain and humidity. For highly aggressive marine environments with direct saltwater spray or immersion, A4 316 stainless steel is generally the preferred choice. These bolts are well-suited for coastal-adjacent (but not waterfront) installations.

These carriage bolts use standard metric coarse threads per ISO 68-1 / DIN 603. Typical pitches are: M6 × 1.0mm, M8 × 1.25mm, M10 × 1.5mm, M12 × 1.75mm. They are compatible with any standard metric hex nut and flat washer of the matching diameter. No special tooling is required.

A carriage bolt (coach screw / cup square bolt) has a smooth, domed head with a square shank section directly beneath it. When driven into timber, the square section bites into the wood and prevents the bolt from rotating, so you only need a wrench on the nut side. This makes them ideal for wood-to-wood and wood-to-metal connections where one face is inaccessible. A standard hex bolt requires a wrench or socket on both ends.

A flat washer under the nut is generally recommended to distribute the clamping load and protect the surface of the material. The domed head side typically does not require a washer. Using a washer also helps prevent the nut from pulling through softer or thinner materials. For best results, use an A2 stainless steel washer to match the bolt material and avoid galvanic corrosion.

Yes. A2 304 stainless steel is generally compatible with modern ACQ (Alkaline Copper Quaternary) and CA (Copper Azole) pressure-treated lumber. Unlike standard zinc-plated or hot-dip galvanized hardware, stainless steel resists the accelerated corrosion that copper-based treatment chemicals can cause. Always check the lumber manufacturer's fastener recommendations for your specific treatment type.