Primitive "Free-Bolt" Screw-Key P-Lock

This is a primitive (in design and execution) screw-key "P-lock." Unlike the one shown nearby by Kevanrabat, which has its bolt withdrawn from the shackle, against an internal spring, by the threaded key, this lock has a completely "free" bolt which threads into the shackle and is removed by unscrewing it with the key; once opened it is not retained inside the lock, the obvious disadvantage being that it can easily be lost. Note that in the evolution of this design the female threads were moved from the hole in the Shackle and re-located to the inside of the Key. In the later version, as shown by Kevanrabat, the key threads onto the bolt until a collar stops it at the lock's body. As it continues to turn, the bolt continues to be drawn into the key withdrawing it from the unthreaded hole in the shackle. (The shackle-end of the bolt is square and passes through a square hole in a plate mounted inside the lock, thus preventing the bolt from rotating along with the key. In the earlier version, shown above, the "square bolt & hole" idea is represented by the pyramidal end on the bolt and corresponding hole in the key.)