Interrupted screw

An interrupted screw or interrupted thread is a mechanical device typically used in the breech of artillery guns. It is believed to have been invented in 1845.

It is a screw that has a section of thread along its axis removed. The screw is mated with a partially threaded hole at the rear of the weapon's chamber: where the screw has threads the hole has none, and vice versa. The screw can thus be smoothly inserted all the way into the gun, after which as little as one-sixth of a turn can engage the two sets of threads securely, sealing the breech. Interrupted screws are occasionally seen in loose gunpowder rifles, as this mechanism was historically one of the few practical ways to achieve a gas-proof seal with a breech-loading firearm that does not employ cartridges. An earlier method was the use of a wedge to block the rear of the gun.