Carriage Bolts

Carriage bolts, also known as coach bolts, are robust fasteners distinguished by a low-profile, mushroom (dome) head and an integrated square or ribbed neck. The primary engineering purpose of a carriage bolt is to provide a self-locking, heavy-duty connection for wood-to-wood or wood-to-metal assemblies. When seated into a pre-drilled hole, the square neck bites into the substrate, locking the bolt in place and preventing rotation. This ingenious design allows for high-torque nut installation from a single side while presenting a smooth, tamper-resistant exterior.

Materials and Finishes

Carriage bolts are subjected to rigorous environmental and structural demands, requiring highly resilient construction. They are primarily forged from Carbon Steel, Stainless Steel, and Specialty Alloys. To prevent degradation from weather, moisture, or chemical exposure, these bolts are offered in a variety of robust finishes, including Zinc Plated, Hot-Dip Galvanized, Black Oxide, Zinc Flake Coating, PTFE, and Phosphate and Oil.

Technical Specifications and Standards

To guarantee safety and load-bearing integrity in construction and infrastructure, carriage bolts adhere to strict international engineering specifications.

• Standards: Compliant with DIN 605, ISO 8677, DIN 603, ASTM F593, DIN 607, ASTM A193, ASTM A307, and DIN 608.
• Head and Neck Styles: Characterized by a Mushroom (Dome) Head and a self-locking Square Neck.
• Grades: Available in metric grades 3.6, 4.8, 8.8, and stainless variants A2-50, A2-70, A4-70, and A4-80.
• Mechanical Properties: Engineered for Tensile Strengths between 60,000 psi and 120,000 psi, Yield Strengths from 36,000 psi to 92,000 psi, and Hardness spanning Rockwell B69 to B100.
• Thread Types: Available in an array of threads including UNC, UNF, UN, ISO Metric, BSW, and ACME.
• Special Features: The integrated neck enables self-locking in wood materials.

Applications and Industries

Thanks to their smooth, snag-free heads and one-sided installation, carriage bolts are highly favored in structural, outdoor, and public-facing applications:

• Timber Construction: Securing structural beams, decking, fencing, and heavy wooden frames.
• Public Infrastructure: Fastening park benches, playground equipment, and public transit seating where a tamper-resistant, flush surface is critical.
• Marine and Coastal: Stainless steel carriage bolts are used in docks and marine structures for severe corrosion resistance.
• Automotive and Trailers: Bolting wooden truck beds and trailer flooring to metal chassis.

Conclusion

Carriage bolts offer an elegant yet powerful fastening solution, effortlessly blending structural strength with tamper resistance. Their self-locking capability and smooth aesthetic finish make them an indispensable choice for heavy timber framing and security-critical public installations.