M6 M8 COACHs CUP SQUARE DOME CARRIAGE BOLTS SCREWS A2 304 STAINLESS STEEL

M6 refers to a 6 mm thread diameter and M8 to an 8 mm thread diameter. M6 bolts are suited for lighter structural connections — thin timber panels, furniture joints, and enclosure hardware — while M8 bolts provide greater clamping force and shear resistance for heavier timber framing, gate hinges, and load-bearing assemblies. When in doubt, match the bolt diameter to the pre-drilled hole size in your hardware or hinge plate.

A2 304 stainless steel has a minimum tensile strength of approximately 500 MPa (property class 50 per ISO 3506), which is comparable to a Grade 4.8 carbon steel bolt. Zinc-plated steel bolts in Grade 8.8 will be stronger in raw tensile terms, but A2 stainless offers significantly better corrosion resistance without relying on a surface coating that can chip or wear. For outdoor, coastal, or humid environments, A2 stainless is the more durable long-term choice.

A2 304 stainless steel forms a passive chromium oxide layer that resists rust in most outdoor and freshwater environments. It performs well in rain, humidity, and general weather exposure. For direct saltwater or chloride-heavy environments (coastal splash zones, swimming pool surrounds), A4 316 stainless would be the recommended upgrade. In standard garden, decking, and outdoor furniture applications, A2 304 provides reliable long-term corrosion resistance.

A washer under the nut is recommended whenever the bolt passes through a material softer than the nut face — timber, plywood, or composite board. The washer distributes the clamping load over a wider area, preventing the nut from pulling through the material under load. The dome head side does not typically require a washer as the cup profile already provides a broad bearing surface against the workpiece.

A general rule is to select a bolt length equal to the total thickness of all materials being clamped, plus enough thread engagement for the nut — typically 1.5× the bolt diameter as a minimum. For example, clamping two 18 mm timber boards (36 mm total) with an M8 bolt would call for at least a 50 mm bolt to allow the nut to fully engage. Always account for any washer thickness in your calculation.

Yes, with the right approach. In aluminum extrusion frames, carriage bolts are typically used with T-slot nuts or drop-in nuts seated in the extrusion channel — the square neck may not self-lock in metal, so the bolt should be held manually or with a small clamp during nut tightening. For PC case panel fastening, the dome head provides a clean exterior finish. Confirm the thread pitch (M6 × 1.0 or M8 × 1.25) matches your T-nuts or threaded inserts before ordering.

Yes. These bolts use standard ISO metric coarse thread — M6 × 1.0 mm pitch and M8 × 1.25 mm pitch — which is compatible with any standard metric hex nut, flange nut, wing nut, or coupling nut of the matching size. No special tooling or proprietary hardware is required.