M4 M5 M6 M8 Stainless Steel Carriage Bolts | A2 Cup Square Screws DIN 603

As a general rule, the bolt should be long enough to pass through all materials being joined plus at least one full nut thickness. For example, joining two 20mm (approx. 3/4") boards typically requires a bolt of at least 50mm (approx. 2"). Always add 5–10mm of thread engagement beyond the nut for a secure hold. Bolt length on DIN 603 carriage bolts is measured from under the head to the tip.

These bolts follow the ISO metric coarse thread standard per DIN 603. M4, M5, M6, and M8 refer to the nominal thread diameter in millimeters. They are compatible with standard ISO metric hex nuts and flat washers of the corresponding size, which are widely available at hardware stores across the US.

Yes. A2 stainless steel (304 grade) generally offers good corrosion resistance in most outdoor environments including rain, humidity, and mild coastal exposure. For highly aggressive marine or saltwater environments, A4 (316) stainless is typically recommended. These bolts are well-suited for decking, fencing, pergolas, and outdoor furniture in most US climates.

A2-70 stainless steel carriage bolts typically have a minimum tensile strength of 700 MPa (approx. 101,500 psi). This makes them suitable for structural wood connections, timber framing, furniture assembly, and general construction where moderate load-bearing is required. For heavy structural applications, consult an engineer for load calculations.

A carriage bolt (DIN 603) has a smooth domed head and a square shank section beneath it that bites into wood to prevent rotation during tightening — no wrench needed on the bolt head. A hex bolt has a hexagonal head requiring a wrench on both ends. Carriage bolts are preferred for wood-to-wood and wood-to-metal connections where a clean, tamper-resistant finish is desired.

Yes. These carriage bolts are designed to be used with a standard ISO metric flat washer and hex nut on the threaded end. The square neck under the head locks into the material, so you only need to tighten the nut from one side. Using a washer is recommended to distribute load and protect the surface finish of your workpiece.

You can choose from pack quantities of 2, 5, 10, 20, 50, or 100 bolts. Packs of 2–5 are ideal for small repairs or prototyping. Packs of 10–20 suit typical furniture or gate projects. Packs of 50–100 offer the best per-unit value for deck construction, fencing runs, or production woodworking.

The anti-rotation square neck is designed primarily for wood and soft composite materials where it can embed and grip. In metal or hard plastics, the square neck generally does not bite in — in those cases, you would typically need to hold the bolt head with a tool or use a different fastener type. For wood-to-metal connections, the square neck grips the wood layer while the bolt passes through a pre-drilled hole in the metal.