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Carriage Bolt vs. Hex Bolt: What Are the Main Differences?


Posted on August 3, 2023

Fastener Systems Inc. is here to help you make the best choice. With our extensive selection of bolts and other fasteners, we can ensure that you will find the perfect fit for your project.

Bolts, one of the most versatile and reliable types of fasteners, play an integral role across countless applications and industries. Among the various types of bolts, hex bolts and carriage bolts represent two popular choices due to their distinctive characteristics and uses.

Carriage Bolt vs Hex Bolt

This article will deal with the differences between a carriage bolt and a hex bolt and will provide the information necessary to make the best choice for a given project.

Hex Bolts Explained

Hex bolts, also called hexagonal head bolts, have heads that are shaped like a hexagon. You can use a wrench or socket to tighten or loosen them. Hex bolts come in different sizes and materials, so they can be used in many different situations.

Among the types of hex bolts, hex machine bolts are noteworthy as they are commonly used in heavy-duty applications due to their strength and precision. Unlike other bolts, hex machine bolts do not drill through materials themselves; they work in concert with pre-drilled and tapped holes to establish a strong, stable bond.

When inserted into a tapped hole and secured with a nut, the tension generated causes the bolt to stretch, thereby reinforcing the bond.

Carriage Bolts Explained

Carriage bolts, alternatively referred to as coach bolts, are another prevalent type of bolt. They feature a rounded head, which is usually square underneath, and a cylindrical shaft that may be fully or partially threaded. The distinctive design of the head allows it to sink into the material and prevents it from moving or turning, which makes it ideal for use in wood and other similar materials.

The square section beneath the head locks into the material to prevent rotation during the tightening process, which differentiates it from other bolt types, and requires a unique installation process. This feature, combined with the bolt's smooth, domed exterior, makes carriage bolts a popular choice for applications that demand a clean finish.

Comparing Hex Bolts and Carriage Bolts

When comparing hex bolts to carriage bolts, it's essential to understand their key differences. The primary distinction between the two lies in their design and, as a result, their ideal applications.

Carriage Bolts - Advantages

Self-locking Mechanism

The square cross-section just beneath the head of a carriage bolt allows it to fit into a square hole, which makes it self-locking when used in a square hole in a metal strap. This design advantage allows the fastener to be installed using only one tool, from one side of the material.

Single-sided Removal

The carriage bolt is commonly used in security applications where the bolt must be removable from one side only. The smooth, domed head and the square neck prevent the bolt from being gripped and rotated from the insecure side.

Strong, Non-rotating Hold

Carriage bolts are effective in fastening wood to metal, and wood to wood due to the square section under the head that provides enough grip to prevent rotation when used in bare timber.


Carriage bolts can be used in various industries, such as water conservation and treatment, railroad, farming, and mining. They are also suitable for use in different applications such as fastening metal to metal, wood to metal, and wood to wood.

Ease of Installation

Carriage bolts are designed to be inserted into pre-drilled holes. Once the bolt is inserted into the hole (by hand or gently with a hammer if needed), a washer and nut are attached to secure the bolt. The washer helps to prevent damage when the nut is used to pull the bolt through the material.


Carriage bolts possess both tensile and shear strength, which depends on the grade and material of the fastener. This contributes to the bolt's durability and the secure hold it provides.

Carriage Bolts - Disadvantages

Not Suitable for Fine Furniture or Cabinetry

Carriage bolts are often not ideal for fine furniture or cabinetry due to their size, which can make them difficult to hide. This can impact the aesthetic appeal of a project where a more hidden or discreet fastening solution would be preferable.

One-Side Accessibility

While an advantage in some situations, the design of carriage bolts, with a rounded head and the tightening completed by twisting the nut over the thread, means they can only be accessed and tightened from one side.

Difficulty in Countersinking

The design of the carriage bolt also expects the head to sit on top of the material.

Limited Material Compatibility

While carriage bolts are compatible with multiple materials, including wood and metal, they may not be suitable for all material types or applications, such as certain types of plastic or composite materials.

Hex Bolts - Advantages

Hex Bolts - Advantages

Six-Sided Head Design

The hexagonal-shaped head is the most distinctive feature of a hex bolt, hence its name. This design allows for a secure grip with a wrench or a socket, and provides a broad surface area for tools to apply torque.


They are ideal for heavy-duty fixing and fastening applications, and their uses span from construction projects to machinery assemblies, woodworking tasks, engineering applications, and vehicle or automotive repairs.


Hex bolts offer strong tensile properties. They are designed to bear heavy loads, which makes them ideal for applications that demand strength, such as the construction of buildings, bridges, and road infrastructures.

Choice of Types and Sizes

Hex bolts are available in various types and sizes, including both fully and partially threaded variants.

Different Materials and Finishes

Hex bolts come in various materials and finishes, such as stainless steel, carbon steel, and more, which allows them to be used in different environments and scenarios.

Hex Bolts - Disadvantages

Potential for Stripping

If too much force is applied when tightening or loosening a hex bolt, it is possible to strip the corners of the hexagonal head. This can make the bolt difficult to remove and might require specialized tools or methods for extraction.

Not as Aesthetically Pleasing

Hex bolts have a more industrial appearance, which may not be suitable for all applications, particularly those where the fasteners are visible and aesthetics are a consideration.

Protruding Head

Unlike countersunk screws or certain other types of fasteners, hex bolts have a head that protrudes from the surface of the material. This can be a disadvantage in applications where a flush surface is desired or where the bolt could be a snag hazard.

Choosing the Right Bolts - Find Your Solution with Fastener Systems

Fastener Systems Inc. is here to help you make the best choice. With our extensive selection of bolts and other fasteners, we can ensure that you will find the perfect fit for your project.

Contact us today or checkout our catalog of our entire range of fasteners and tools!