Carriage bolt

A carriage bolt (also called coach bolt and round-head square-neck bolt is a form of bolt used to fasten metal to metal or metal to wood.

Carriage bolt has a square shoulder under a rounded head which resists turning when the nut is tightened or removed. They are good for wood-to-wood connections when the head may not be accessible for tightening. They may be used in the construction of docks, swing sets and decks as well as other surfaces where a smooth finish is needed.