Carriage bolt

[2] This makes the bolt self-locking when it is placed through a square hole in a metal strap.

It is common to use a carriage bolt on bare timber, the square section giving enough grip to prevent rotation.

The smooth, domed head and square nut below prevent the carriage bolt from being gripped and rotated from the insecure side.

Instead of the carriage bolt's square part of the shank immediately under the head, the timber bolt has four fillets, whose sharp corners grip the edge of the hole in the wood to prevent rotation.

Such bolts continue to be used to hold shovels onto cultivators, and cutting edges onto earthmoving implements .