steps of successively larger radius. For example, this allows a breechblock with four steps to allow four-fifths of the block circumference to be threaded, allowing for a much shorter breechblock while still requiring only one-fifth of a turn to open or close. This is the basic design still in use with bagged charge artillery. 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 metallic cartridges. An earlier method was the use of a wedge to block the rear of the gun. The system has also been used to close other applications, including the joint between helmet (bonnet) and breastplate (corselet) of standard diving suit helmets, and the locks of diving chambers. References External links Interrupted Screw Breech Mechanisms Precision Screwdriver Set Manufacturing Interrupted Threads Used On Naval Guns Screws Firearm components