The Beginner’s Guide to Carriage Bolts

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When shopping for bolts, you may come across carriage bolts. Also known as coach bolts, they are used in fastening applications. You can use carriage bolts to fasten metal workpieces to other metal workpieces, or you can use them to fasten wooden workpieces to metal workpieces.

What Are Carriage Bolts?

Carriage bolts are heavy-duty threaded fasteners with a low-profile, mushroom-shaped head. They originated in the early 19th century. As their name suggests, carriage bolts were initially used on carriages. Carriages — particularly the wheels of carriages — required special fasteners that could withstand heavy usage. This led to the development of the modern-day carriage bolt.

Horse-drawn carriages have since faded in favor of faster and more efficient methods of transportation. Nonetheless, carriage bolts continue to be used in fastening applications.

Carriage Bolts vs Other Bolts

You might be wondering how carriage bolts differ from other types of bolts. After all, they still have a threaded shank, and carriage bolts still have a head on top of their respective shank. While they may look like most other bolts, carriage bolts are distinguished from their standard counterparts in several ways.

One of the main differences between carriage bolts and other types of bolts is the head. Carriage bolts feature a low-profile head that’s shaped like a mushroom. In comparison, other types of bolts may feature a higher-profile head in a hexagonal shape.

When inspecting a carriage bolt, you may notice that it has a square- or hexagonal-shaped band directly under its head. The head is still shaped like a mushroom, but the threaded shank directly under the head has a square- or hexagonal-shaped band. This band allows carriage bolts to lock into place when inserted into a hole of the same shape.

Benefits of Carriage Bolts

Carriage bolts are prized for their strength and durability. They are stronger and more durable than most other types of bolts.

You can find carriage bolts in different thread styles. All carriage bolts have threading on the shank. With that said, some carriage bolts have a fully threaded shank, whereas others have a partially threaded shank. A partially threaded shank means that only some of the shank — typically about three-quarters of the shank — is covered in threading.

Carriage bolts can lock into place. Most carriage bolts feature a band directly under the head. As previously mentioned, this band allows them to lock into place. Inserting a carriage bolt into a hole of the same band shape will lock it in place.

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