Are you in the middle of a building project and not sure what type of fastener to use?
The fastener isles in hardware stores can be quite overwhelming if you don’t know what you are looking for. There are nuts, bolts, and screws of different sizes, shapes, and materials. Sometimes it’s difficult to know where to start.
This article will discuss carriage bolts and give you everything you need to know about them.
What Is a Carriage Bolt?
A carriage bolt is a type of fastener that joins two pieces of material together. It’s characterized by a rounded, low-profile head that sits flat on a surface. Beneath the head is a square section of the neck, although this can vary depending on the exact type of bolt used. Further down the neck is the thread.
Combined with a nut, the carriage bolt works to clamp two pieces of material together. Frequently, this is two wood components, as well as metal. Although there are more applications.
To learn more about how it works, read my guide on how to install a carriage bolt and how to remove it.
Advantages and Disadvantages of Carriage Bolts
The application of carriage bolts is varied. Some situations are better to use them than others.
Advantages of Carriage Bolts
The main advantages of carriage bolts include:
- They are self-locking – the square section of the shank will stop the bolt from turning during installation.
- The rounded head is a cleaner finish than standard bolts.
- In furniture applications, a carriage bolt is less dangerous than standard bolts. People will not catch themselves easily on the rounded surface.
- Compatible in a range of situations, with multiple materials, including wood and metal.
- Shear strength varies depending on the type of carriage bolt used. However, they are a strong fastener, especially when compared to smaller fixings.
Disadvantages of Carriage Bolts
The main disadvantages of carriage bolts include:
- The bolt, generally, isn’t good for fine furniture or cabinetry. This is mainly due to the size, they are difficult to hide. However, they are preferable to standard bolts.
- Carriage bolts can only be accessed from one side. The rounded head means that tightening is completed by twisting the nut over the thread.
- The design of the carriage bolt is for the head to sit on top of the material. This means countersinking the head slightly, to reduce the profile and improve appearance, which can look awkward.
4 Common Carriage Bolt Uses
A carriage bolt can be used in a lot of different situations. If you want to use a carriage bolt for a structure, make sure to consult with a structural engineer. You must make sure the fasteners are strong enough to support the weight of the structure.
1. Wooden Framing
Constructing with wooden frames is one of the most common building methods used. Traditionally, frames were cut to interlock together, without the use of fasteners. Now, with more modern building techniques, fasteners are a staple of wood framing.
Carriage bolts lend themselves very well to wooden framing. Especially so in areas where people frequently walk, or brush, past the component. For example, if building a climbing frame, a jagged bolt head, with its sharp corners, is more of a hazard than a carriage bolt.
2. Jointing Metal and Wood
The design of carriage bolts also means that different material types can be jointed. Fixing wood and metal together means that hybrid constructions become possible. This lets us use stronger material where it’s needed, lighter material where possible, and also cheaper material in particular situations.
3. Other Carriage Bolt Uses
The options to use carriage bolts are almost endless, below are five more very common applications:
- Decking
- Pontoons and docks
- Internal and external partitions
- Playground furniture and equipment
- Locks and security doors
4 Carriage Bolt Types
Not all carriage bolts are the same. Below are the four main types you can find in stores.
1. Square Neck Carriage Bolts
These carriage bolts are often thought of as the “standard.” A square neck carriage bolt has the same smooth, domed, head. Just underneath the head, the neck turns square, which gives the bolt its name.
2. Ribbed Neck Carriage Bolts
The ribbed neck carriage bolt has one key feature that differentiates it from the square neck. On a ribbed neck carriage bolt, the neck has a series of vertical ribs instead of the square. The function of the ribs is the same as the square, to stop the bolt from turning whilst it is tightened.
3. Long Neck Carriage Bolts
If the bolt must pass through thick material, a long neck is required. This provides suitable clearance for the nut to get fastened securely onto the bolt’s thread.
4. Short Neck Carriage Bolts
When jointing two thin pieces of material, a shorter neck is needed. Often, the short neck carriage bolt is used on sheet metal. If a standard size carriage bolt is used, there would be too much of the neck protruding out of the material, which is a hazard and obstruction.
3 Carriage Bolt Alternatives
The world of fasteners is huge. Sometimes there is a better alternative to a carriage bolt, depending on the situation. Other times, you might not have access to carriage bolts and need to find another option.
Below are just a few of the alternatives you might want to consider.
1. Screws
Similar to a carriage bolt, screws fix material together with a clamping action. Screws come in a range of sizes, shapes, and materials. The advantage screws have over carriage bolts is the speed they can be applied in.
Also, screws tend to be smaller than bolts. This can be both an advantage and a disadvantage. A screw can be used in situations where a carriage bolt is too large. However, the shear strength of a screw, in general, is less than a bolt.
2. Elevator Bolts
An elevator bolt is quite similar to a carriage bolt. However, there is one key difference. The top of the head is flat, and the underneath is rounded. This allows the elevator bolt to sit flatter, with a lower profile. As the name suggests, they are often used in elevator systems.
3. Hex Bolts
If you imagine a bolt, chances are the one that comes into mind is a hex bolt. They are the most widely used bolt around the world. The head of the bolt is hexagonal, to allow a spanner or a wrench to fit over it and tighten.
In a separate article I wrote in detail about how carriage bolts and hex bolts compare.
4. Lag Bolts
Even though they are often called bolts, lag bolts are – in fact – screws. That’s because they are designed to drive themselves into wood. That said, compared to regular screws, they are much thicker and thus also much stronger. Furthermore, rather than being tightened with a screwdriver, they feature a hex head like bolts.
To learn more about whether this is the right type of fastener for you, read my comparison of carriage and lag bolts.
Summary
Carriage bolts are an amazing type of fastener. The fixing comes in a range of sizes and materials, which means that it can be used in a lot of different situations.
The bolt’s smoother, lower-profile head is a safer and cleaner finish – particularly if people will come into close contact with it.