What Is A Carriage Bolt

Carriage bolts are a type of bolt used in woodworking, mostly in joining wood to metal. Despite being intended for use with wood, carriage bolts have a machine screw thread, and are commonly used to join metal to metal. Carriage bolts have a large domed mushroom head, with a square section right underneath the head.

The domed mushroom head prevents the bolt from being pulled through a wooden construction and prevents removal/loosening from one side. The domed head does mean that carriage bolts cannot be installed by screwdriver bits or a socket and spanner.

The square section under the head of a carriage provides a level of locking ability when tightening into soft materials such as wood. This allows the fastener to be installed with only one tool, a spanner or wrench, working from one side.

 

 

A popular reason for using carriage bolts is their round head, which can give a finished appearance for many builds uses. This aesthetic appeal sees them used in everything from outdoor wooden stairs and steps to flush faces surfaces in the automotive and transport industries.