A locking pin is a small device that's used to stop a nut from turning and to help lock it in place for extra security.

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Put the bolt in place by putting it through two pieces of metal that you want held together. Locking pin bolts are bolts that have a hole drilled through the shaft of the appropriate size to accommodate a locking pin being pushed through. Other than the hole though, these bolts work the same way as regular bolts do.

Screw on a nut. The nut should be tightened up until it is past the hole in the locking bolt's shaft so that you can still put the pin through. However, there shouldn't be too much room, no more than 3-4 turns of the nut, between the hole and where it presses up against the metal to hold it together with the bolt.

Pull the pin out of the locking pin's shaft. The locking pin is a cylinder that's like a bolt without threads and pushed through the end of the cylinder is a pin attached to a ring. Pull out the pin so that the shaft can easily slide through the hole in the bolt. Once the main cylinder is through, push the pin back through the hole and lock it in place. Try to pull the locking pin out to make sure that it's solidly in place.