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What is a Carriage Bolt?
Carriage bolts are a special bolt with a round head and a square neck, usually used for fastening connections between wood and metal. Its main features include:
Round head design, no exposed edges and corners to prevent scratches or hooks;
Square neck structure, embedded in wood or metal during installation to prevent the bolt from rotating;
Often used with nuts to form a reliable fastening connection.
Carriage bolts are widely used in woodworking, construction, agricultural equipment, railways, bridges and other fields due to their unique structure.
Structural characteristics of carriage bolts
Bolt head: semicircular or smooth dome to avoid hooking or damaging surrounding objects.
Square neck part: located below the bolt head, usually square, can be embedded in the hole of wood or metal to prevent the bolt from rotating when tightened.
Threaded rod: full thread or partial thread, suitable for different fastening needs.
Main application scenarios of carriage bolts
1. Carpentry and construction industry
Used for connecting beams and columns of wooden structures to prevent bolts from rotating;
Splicing and fixing outdoor wooden fences, wooden bridges, and fences;
Applicable to wooden furniture, playground facilities and other occasions.
2. Machinery Manufacturing
Used for metal-to-metal connections in conveying equipment, industrial racks, etc.;
Fixing steel plates and brackets in railway and bridge construction;
Fasteners in agricultural equipment (such as tractors and tillers).
3. Automobile and shipbuilding industry
Applicable to the fastening connection of vehicle frames and chassis components;
Stainless steel carriage bolts are used in dock facilities and marine equipment to improve corrosion resistance.
4. DIY & Home Improvement
Commonly used for assembling wooden flower stands, swings, outdoor benches, etc.;
Reinforcement of home fences, doors and windows.
How to install a carriage bolt
1. Drilling preparation
Make sure the drill hole diameter matches the square neck of the carriage bolt to prevent rotation.
2. Insert the bolt
Knock the bolt head into the hole so that the square neck is embedded in the wood or metal hole to achieve anti-rotation fixation.
3. Tighten the nut
Use with hexagonal nuts or flange nuts to ensure stable fastening.
Notes:
For harder materials, tap the bolt head in the hole to ensure that the square neck is fully engaged;
For high-strength fastening, use spring washers and anti-loosening nuts to prevent the bolt from loosening.
Production process
1. Cold heading: Use high-speed cold heading machine to form bolt head and square neck at one time to improve production efficiency.
2. Thread processing: Use rolled thread to improve strength and fatigue resistance.
3. Heat treatment: For high-strength carriage bolts (such as grade 8.8, grade 10.9), quenching + tempering is performed to improve durability.
4. Surface treatment: Select anti-corrosion coatings such as galvanizing, Dacromet, stainless steel polishing, etc. according to the application environment.
5. Quality inspection: Including dimensional tolerance, tensile strength, torque testing, etc. to ensure compliance with industry standards.
Industry Standards
ISO 8677: International standard that specifies the dimensions, tolerances and performance requirements for metric carriage bolts.
DIN 603: German standard that defines the dimensions and material properties of carriage bolts.
ANSI/ASME B18.5: American standard that applies to carriage bolt specifications for the North American market.
GB/T 14: Chinese national standard, commonly used in the construction and machinery industries.
How to choose the right carriage bolt?
1. Choose materials according to the application
Indoor applications: ordinary carbon steel galvanized bolts are sufficient;
Outdoor wood structures: choose hot-dip galvanized or Dacromet carriage bolts;
Marine/chemical environment: 304 or 316 stainless steel carriage bolts are more corrosion-resistant.
2. Choose the appropriate bolt length
Calculate that the bolt shank should at least penetrate the connected parts and leave enough threads to tighten the nut.
3. Determine the surface treatment
For humid environments, hot-dip galvanizing is more corrosion-resistant than electroplating;
Dacromet coating is suitable for high-temperature environments (such as automotive engine parts).
4. Is additional anti-loosening design required?
In high-vibration environments, anti-loosening nuts, spring washers or coated thread lockers can be used.
With its unique round head + square neck design, carriage bolts play a key role in many fields such as woodworking, construction, mechanical equipment, and the automotive industry. Choosing the right material, length, surface treatment, and anti-loosening measures can ensure the firmness and service life of the connection.
