Carriage Screw

What Are Carriage Screw?

Carriage screws are a type of hexagon bolt specialised for use in woodworking, in particular, fastening metal to wood. Carriage bolts are designed with a domed head, which can prevent loosening from one side, an enlarged head shape also prevents the bolt from being pulled through a wooden construction. The presence of a domed head does mean that carriage bolts cannot be installed by methods which push the bolt axially during installation, such as a spanner drill adaptor.

The square head section of a carriage bolt allows it to be installed using a spanner, for improved leverage. A square section also provides some level of locking ability when tightening into soft materials such as wood. An unthreaded section below a carriage bolt’s square section adds strength and resistance to shear forces.

The downside of carriage bolts is that their head shape makes them incompatible with torque wrenches and drill adaptors.

Carriage bolts also provide several secondary benefits, such as the aesthetic appeal of their rounded head, which can give a finished appearance to many applications. Despite being intended for use with wood, carriage bolts have a machine screw thread, and are equally suitable for metal applications. However, carriage bolts may be more difficult to install due to their incompatibility with drill adaptors.