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. 316 marine grade stainless steel is the choice for severe enviroments that require a high level of corrosion resistance. Type 316 stainless steel is the preferred material used in the marine enviroment and boating industry due to its resistance to pitting corrosion. 316 stainless steel has high resistance to corrosion from sea sealt water and industrial chemicals.