M10 x 200mm
A Coach Bolt or Carriage Bolt is a form of bolt used to fasten metal to wood.
It is distinguished from other bolts by its truss 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. This allows the fastener to be installed with only a single tool, a spanner or wrench, working from one side.