A carriage bolt, coach bolt or round head square neck bolt is used through iron strengthening plates on either side of a wooden beam. It is commonplace though to use them on bare timber, the squared section giving enough grip to prevent rotation. Carriage bolts are extensively used in security fixings where the bolt must only be removable from one side. The smooth domed head and square neck below prevent the carriage bolt from being unlocked from the insecure side. A Galvanized coating is the process of applying a protective layer of zinc that prevents rusting. These bolts are coated by the hot dip galvanizing process, in which they are dipped into a bath of molten zinc. These fasteners are a great choice for use with pressure treated wood or any application that is exposed to elements that may cause corrosion.