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Carriage Bolts.

Carriage Bolts

What are Carriage Bolts?

Carriage bolts, distinguished by their round, domed head with a square section underneath, are an essential component in precision engineering and assembly. This unique design allows the bolt to self-lock when inserted into a square hole or a round hole in a softer material that will allow the square undercut to bite into the material forming its own recess. The smooth, rounded head offers an aesthetic finish, making them ideal for use in exposed applications where appearance is important.

How Carriage Bolts Work.

Carriage bolts and nuts are versatile fasteners, commonly employed in wood construction, including outdoor furniture, decking, and fencing. As the name suggests, traditionally they were used in assembling horse-drawn carriages.

The square section beneath the bolt's head digs into the material, preventing the bolt from turning as the nut is tightened. This feature is particularly advantageous in scenarios where access to the bolt head is limited, like securing a wheel onto a cart or assembling a wooden play structure, where only one side is accessible for tightening.

Materials of Carriage Bolts.

Accu's range of carriage bolts are available in A2 and A4 stainless steel, renowned for their corrosion resistance and durability. A2 stainless steel offers excellent resistance in typical indoor environments, while A4 is preferred for marine and outdoor applications due to its enhanced corrosion resistance. These materials ensure longevity and reliability in various applications, from architectural design to machinery manufacturing.

Sizes and Types of Carriage Bolts.

We offer carriage bolts in sizes ranging from palm-sized M5 (5mm) to robust M16 (16mm), with lengths spanning from 25mm to 300mm, catering to a wide range of industrial requirements.

Our selection includes relfection-free black carriage bolts, treated with AccuBlack chemical blackening for an elegant and corrosion-resistant finish. Additionally, we offer AccuLock thread-locking patches for enhanced security, and custom manufacturing options for specific needs.

In related product categories, consider exploring our range of hex bolts which offer different head styles and functionalities, primarily focused on the ability to tighten these bolts from the head.

Carriage Bolts Vs. Coach Bolts.

Often used interchangeably, both carriage and coach bolts are one and the same. The confusion begins when you learn that there are also lag bolts, lag screws and coach screws which are actually self-tapping screws with a hexagon head. For a detailed explanation of coach bolts, carriage bolts and lag bolts, please take a look at our article discussing the differences between these fasteners.


Q: How to remove carriage bolts from wood?.

A: To remove a carriage bolt from wood, apply gentle, consistent force to unscrew the nut and avoid damaging the wood. Pay close attention to if the bolt begins to spin as this can result in damaging the wood. If the bolt is rusted, applying a penetrating oil beforehand can ease the process.

To remove a carriage bolt that keeps spinning, apply downward force to the bolt head while unscrewing the nut which may provide enough friction to begin loosening. If accessible, use tools like locking pliers or a wedge to grip the bolt's smooth head. In cases where the head isn't accessible, carefully cutting a slot in the bolt's head with a rotary tool to use a flathead screwdriver can provide the necessary grip.

Q: What is a carriage bolt used for?.

A: Carriage bolts are ideal for wood construction, such as decks and fences, and metal-to-wood connections, featuring a smooth, rounded head for reduced snagging risks and aesthetics. They are designed for easy tightening from one side, especially in hard-to-reach areas.

Q: What are the advantages of using A4 stainless steel carriage bolts?.

A: A4 stainless steel carriage bolts offer exceptional corrosion resistance, making them ideal for marine and harsh outdoor environments. Their durability and longevity in challenging conditions make them a preferred choice for long-term applications.

Q: Can carriage bolts be used for metal-to-metal applications?.

A: While carriage bolts are primarily designed for wood-to-wood or metal-to-wood connections, they can be used in metal-to-metal applications provided the receiving material has a square hole to accommodate the square section under the bolt head, ensuring proper locking.

Q: What is the difference between a carriage bolt and a regular bolt?.

A: Carriage bolts have a round, domed head with no drive and a square section beneath it, allowing them to lock into place without turning. Regular bolts, like hex bolts, require a tool for holding while tightening and are used in a wider range of applications.

Q: Are carriage bolts load-bearing?.

A: Yes, carriage bolts are load-bearing, with their capacity dependent on material, size, and application. They are suitable for structural woodworking and some metalworking tasks, but it's important to match the bolt's specifications with the project's load requirements.

Bespoke Carriage Bolts Manufacture.

High precision, bespoke manufacture of Carriage Bolts to customer specification. State of the art facilities specialising in both small batch prototyping and large scale manufacture.

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