Carriage bolts (also called a coach bolt) is a form of bolt used to fasten metal to metal or metal to wood. Easily identified by a shallow mushroom head and a square shank directly beneath the head. This makes the bolt self-locking when it is placed through a square hole in a metal strap, or when pressed into a hole in wood. This allows the fastener to be installed with only one tool, working from one side. The head of a carriage bolt has a shallow dome shank.

The shank has no threads; and its diameter is equal to the face of the square cross-section.