The lead shot used in shotgun cartridges consists of small spherical pellets 2-3 mm in diameter. The pellets are made by pouring molten lead through a frame pierced with holes which is suspended over a long drop inside a shot tower. The falling lead forms into small spherical drops which solidify and are collected in a tank of water at the bottom of the tower. The size of the shot produced is determined by the size of the holes in the frame and the size of the shot determines the drop height that must be used. Accurately spherical shot has been produced by this method since its invention by William Watts in 1782.