M4 Carriage Bolts – G304 Stainless Steel, DIN 603, Cup Square Dome Head

Generally, select a bolt length equal to the total thickness of the materials being joined, plus enough thread for the nut — typically at least 1.5× the bolt diameter. For M4 bolts, that means at least 6mm of exposed thread beyond the material. Available lengths run from 10mm (3/8") to 30mm (1-3/16"), so measure your stack before ordering.

G304 (A2) stainless steel carriage bolts typically have a tensile strength of around 500–700 MPa, which is generally sufficient for light-to-medium structural and woodworking applications. For heavy load-bearing or safety-critical uses, contact us to confirm suitability for your specific application.

Yes, for most outdoor applications. G304 stainless steel offers good corrosion resistance in rain, humidity, and mild coastal conditions — making it a solid choice for decks, fences, and garden structures. For highly aggressive marine or saltwater environments, G316 stainless steel is generally recommended instead.

These bolts conform to DIN 603 and use standard M4 metric coarse thread with a pitch of typically 0.7mm. They are compatible with any standard M4 metric nut or threaded insert — no special tooling required.

Use a standard M4 metric nut. When fastening into softer materials like wood, plywood, or plastic, placing an M4 flat washer under the nut is recommended to distribute the clamping load and prevent the nut from pulling into the surface over time.

The square section directly beneath the dome head is designed to bite into wood fibers or seat into a matching square hole in metal or composite panels. This locks the bolt rotationally, so you can tighten the nut from one side without needing to hold the bolt head — a key advantage in tight spaces or when working alone.

In most cases, yes. The smooth dome head provides a clean, low-profile finish on the face side. For thin or soft panels, use a backing washer to prevent the square neck from pulling through the material. Contact us to confirm compatibility for specific panel thicknesses or load requirements.