What Is a Carriage Bolt and How Does It Work?

Carriage bolts are a specialized type of fastener that you’ll often see in wood construction, outdoor furniture, fences, and even some metalworking projects. They’re easy to recognize by their smooth, round head and square neck just beneath it. This unique shape isn’t just for looks — it serves a very practical purpose. As a professional carriage bolt supplier, Xinchi is glad to introduce carriage bolts to you.

Structure of a Carriage Bolt: What Makes It Different

A typical carriage bolt has a dome-shaped head that sits flush on the surface of the material. Unlike hex bolts, it doesn’t have any drive recesses for tools. Right under the head is a square neck, and that’s where the magic happens. When inserted into a pre-drilled hole—especially in wood—the square section locks into the material, keeping the bolt from turning as the nut is tightened on the other side.

Carriage bolts come in both fully threaded and partially threaded versions. Full threading gives a better grip for lighter loads, while partial threading is often used when shear strength is a priority.

Carriage Bolt Locking Mechanism: How the Square Neck Prevents Spinning

The square neck on a carriage bolt is key to its function. As the bolt is driven into the material, the square portion bites into the surface, preventing the bolt from rotating when torque is applied to the nut. This makes it ideal for installations where access to only one side of the workpiece is available.

Another benefit of this design is added security. Because the head is round and has no slots for a screwdriver or wrench, carriage bolts are harder to remove from the outside — a common reason they’re used in public or tamper-prone areas like park benches and fencing.

Differences Between a Carriage Bolt and a Hex Bolt

While both carriage bolts and hex bolts are used for fastening, they serve different purposes and are built differently.

Carriage bolts have a round, low-profile head with a square neck that locks into the material. They’re ideal for wood and for applications where only one side of the joint is accessible. You don’t need a tool on the head side once the bolt is locked in place.

Hex bolts, in contrast, feature a six-sided head that requires a wrench or socket for both tightening and loosening. They are better suited to applications where both sides are easy to access and adjustments may be needed later. In general, hex bolts offer more flexibility in mechanical assemblies, while carriage bolts provide cleaner finishes and extra resistance to tampering.

Why Choose Xinchi for Your Carriage Bolt Needs?

At Xinchi Fasteners, we manufacture and supply carriage bolts to strict quality standards, offering a wide selection of sizes, finishes, and materials. Our carriage bolts are available in:

• Zinc-plated, carbon steel, and stainless steel options
• Fully threaded or partially threaded styles
• Custom packaging and bulk quantities

We focus on precision — from cold forging the round heads to ensuring consistent threading and square neck dimensions that hold firmly in wood or metal.

XINCHI is a trustworthy fastener company, especially in furniture nuts. We have a factory,  founded in 2007. We are the designated fastener supplier to“STAPLE”. As a trusted fastener supplier, XINCHI offers a wide range of high-quality fasteners, including nuts, screws, bolts, rivets, and washers. If you would like to learn more about fasteners or are interested in purchasing wholesale fasteners, please don’t hesitate to contact us. Our experienced and expert service team will reply as soon as possible.

With years of experience in exporting fasteners worldwide, Xinchi Fasteners is your reliable source for durable and competitively priced carriage bolts. Clients across construction, furniture, OEM manufacturing, and DIY markets trust us.

Need help selecting the right carriage bolt for your application? Contact our team for technical advice, sample requests, or a quote — we’re happy to help.