Acarriage bolt, coach bolt or round head square neck bolt is a form of bolt used to fasten metal to wood. Its shallow mushroom head and that the shank cross-section of the bolt is circular for most of its length, as usual, but the portion immediately beneath the head is formed into a square section. This makes the bolt self-locking when placed through a square hole in a metal strap, or a round hole in most wood. 

Application: Wind tower, Railway, Automotive industry, Construction, Electronic industry and so on.