A belt or ammunition belt is a device used to retain and feed cartridges into a firearm commonly used on machine guns. Belts were originally composed of canvas or cloth with pockets spaced evenly to allow the belt to be mechanically fed into the gun. These designs were prone to malfunctions due to the effects of oil and other contaminants altering the belt. Later belt designs used permanently connected metal links to retain the cartridges during feeding. These belts were more tolerant to exposure to solvents and oil. Some notable weapons that use belts are the M240, the M249, the M134 Minigun, and the PK Machine Gun.