Carriage bolt

A carriage bolt, coach bolt or round head square neck bolt[1] is a form of bolt.

It is distinguished from other bolts by its head: the shank 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.[2] This makes the bolt self-locking when placed through a square hole, 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. The head of a carriage bolt is usually a shallow dome. The squared section is of the same size as the diameter of the bolt shank, with a plain unthreaded shank.

Carriage bolts were developed for use through iron strengthening plates on either side of a wooden beam. It is commonplace though to use them into bare timber, the squared section giving enough grip to prevent rotation.

Plough bolts

Plough bolt

Plough bolts are a flush-fitting carriage bolt, where the head is countersunk beneath the surface. They were first developed to hold replaceable ploughshares onto the mouldboard of iron ploughs. The share is the most quickly wearing part of the plough and would be replaced several times over the life of the plough.

References

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  1. ↑ Machinery's Handbook (Twenty-First edition ed.). New York: Industrial Press. 1980. p. 1146.
  2. ↑ Machinery's Handbook (Sixth ed.). New York: Industrial Press. 1927. p. 827.