30mm

30 mm is a metric unit of length equal to 0.03 meters (3 centimeters), or about 1.181 inches. It is used to express diameters, thicknesses, and other dimensions in engineering, machining, and manufacturing drawings.

In firearms terminology, 30 mm denotes the caliber, meaning the bore diameter of the projectile. The designation is most closely associated with autocannons used on aircraft and armored fighting vehicles, which fire high-rate-of-fire ammunition across a range of engagement scenarios.

Notable examples of 30 mm applications include cannons such as those mounted on combat aircraft and some ground vehicles. The GAU-8 Avenger, deployed on the A-10 Thunderbolt II, is a widely cited 30 mm design. The M230 chain gun used on the AH-64 Apache is another prominent example of a 30 mm autocannon system.

Ammunition for 30 mm guns covers several types, including high-explosive (HE), high-explosive incendiary (HEI), armor-piercing (AP), and armor-piercing incendiary variants, as well as tracer-equipped rounds. Modern 30 mm rounds are engineered for tasks ranging from air-to-ground bombing to light-armor penetration and suppressive fire, depending on the munition type and design.

Beyond military use, 30 mm appears in civilian contexts as a dimensional specification for components, tools, lenses, fasteners, and other parts where a 30 millimeter diameter or thickness is required.