Carriage Bolt
Carriage bolts, also known as coach bolts, are round-headed fasteners with a smooth, domed head and a square neck underneath. The square neck locks the bolt into place when inserted into a square hole or wooden surface, preventing rotation during tightening. Carriage bolts are commonly used for fastening wood, metal-to-wood assemblies, and structural connections where a smooth, flush surface is needed.
Types of Carriage Bolts
- Standard Carriage Bolt: Domed head with square neck, for wood and light structural applications
- Heavy-Duty Carriage Bolt: Thicker shank and higher tensile strength for industrial and structural use
- Stainless Steel Carriage Bolt: Corrosion-resistant, suitable for outdoor or marine environments
- Hot-Dip Galvanized Carriage Bolt: Enhanced corrosion resistance for outdoor or harsh environments
Applicable Standards
Dimensional Requirements:
- ASME B18.5 – Carriage Bolts (inch series)
- DIN 603 – Carriage bolts (metric series)
- ISO 8677 – Wood fasteners
- ASTM A307 – Carbon steel bolts (general purpose)
- ASTM A193 / A320 – Alloy steel for high-strength applications
Material Grades:
- Carbon Steel (ASTM A307): Standard strength for general applications
- Alloy Steel (ASTM A193 B7 / B16): High-strength bolts for industrial use
- Stainless Steel (AISI 304 / 316, ASTM A193 B8 / B8M): Corrosion-resistant
- Hot-Dip Galvanized:For enhanced outdoor durability
Material Grades (Commonly Used)
High Tensile, Stainless Steel, Alloy Steel, Inconel, Incoloy, Hastelloy, Monel, Silicon Bronze, Phosphor Bronze, Aluminium Bronze, Nickel, Brass, Copper, Copper Nickel,Duplex, Super Duplex, Titanium Alloys, CB20, Nitronic, Nimonic, ASME, ASTM etc.
Typical Specifications
- Diameter Range: M6 to M36 / ¼” to 1-½”
- Thread Type: UNC / UNF / Metric
- Head Type: Smooth, domed head with square neck
- Shank Type:Full or partial thread as required
- Length: As per application and project specification
Surface Protection / Coating:
- PTFE Coated (Blue, Yellow, Red, Green & Black)
- Hot Dip Galvanized
- Yellow Zinc Plated
- Blue Zinc Plated
- Molykote
- Aluminium Zinc Flake Coated
- Black Phosphate
- Zinc Plated
- Nickel Plated
Engineering Applications
- Wood-to-wood or metal-to-wood connections
- Structural framing and decking
- Outdoor furniture and playground equipment
- Bridges, fencing, and heavy structural timber connections
- Light industrial machinery assembly
Performance & Key Features
- Square neck prevents rotation during installation
- Smooth domed head provides a flush, aesthetically pleasing finish
- Suitable for high-load wood connections and light structural steel
- Corrosion protection options for outdoor or marine environments
- Easy installation with hand tools or power wrenches
Design Considerations
- Ensure square hole or proper seating for anti-rotation
- Select appropriate material grade for strength and corrosion resistance
- Use washers for load distribution on soft materials
- Torque control for optimal clamping without crushing wood or timber