Gas Regulator Key for Lewis Light machine gun, (LMG) .303", serial #A505 (94623). Made by Birmingham Small Arms Co Ltd (BSA), England, for Armes Automatique Lewis Belgium, old serial #94623, (cancelled), DEACTIVATED in May 1977. The Lewis gun featured an adjustable gas system, in which two different gas ports could be selected, L (for large) and S (for small). A lever about 5 inches long was used to rotate the gas regulator 180 degrees to select one port or the other. One end of the lever was machined with a small loop to facilitate grasping, while the other end was machined to be used as a screwdriver for the clamp ring screw. The screwdriver section was normally seated in the gas regulator. During the First World War, it was decided to give the gas regulator key an additional function: it would be turned into a wrench to unscrew the tiny locating stud inside the clamp ring. This is the same purpose behind the modification of the Lewis spanner. The modification involved two steps: the loop end of the key was machined a little thinner on one side, and the round hole of the loop was filed to produce a 0.25-inch square hole. This square hole became the stud wrench. The Lewis gun (or Lewis automatic machine gun or Lewis automatic rifle) is a World War I–era light machine gun of American design that was perfected and widely used by the British Empire. It was first used in combat in World War I, and continued in service with a number of armed forces through to the end of the Korean War. It is visually distinctive because of a wide tubular cooling shroud around the barrel — often omitted in World War I when used on aircraft — and a top-mounted drum-pan magazine. It was commonly used as an aircraft machine gun, almost always with the cooling shroud removed, during both world wars. Action: Gas-operated Rate of fire: 500–600 rounds/min Muzzle velocity: 2,440 feet per second (740 m/s) Effective range: 880 yards (800 m) Maximum range: 3,500 yards (3,200 m) Feed system: 47- or 97-round Pan magazine Sights: Blade and tangent leaf