Interrupted screw
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An interrupted screw or interrupted thread is a mechanical device typically used in the breech of artillery guns. It is a screw that has a section of thread along its axis removed. This removal, coupled with an appropriate hole, allows the screw to be inserted directly and tightened in only 1/4 or 1/6 of a turn. It is sometimes used in loose gunpowder rifles, as it is one of the few practical ways to achieve a gas-proof seal with a gun that uses loose-loaded propellant.