CARRIAGE BOLTES

A carriage bolt, also known as a coach bolt, has a domed or countersunk head, and the shank is topped by a short square section under the head. The square section grips into the part being fixed (typically wood), preventing the bolt from turning when the nut is tightened.

A rib neck carriage bolt has several longitudinal ribs instead of the square section, to grip into a metal part being fixed.