American system of interchangeable parts

Around the 1820s, United States government armories began making firearms whose parts were truly interchangeable. At Harpers Ferry, Virginia, the gunmaker John H. Hall produced breech-loading rifles in which a part taken from any one gun fit any other, checked with a set of steel gauges and cut by specially built machines such as milling machines. The Springfield Armory in Massachusetts, under superintendent Roswell Lee, developed similar methods. British observers later named this the American system of manufactures.¹

The idea was older. In France the gunsmith Honore Blanc had pushed for standardized musket parts in the 1770s and 1780s, and the American Thomas Jefferson, then minister in Paris, wrote about it. Eli Whitney, famed for the cotton gin, promised the US government 10,000 muskets in 1798 and is often credited with interchangeability, but historians find that his famous 1801 demonstration was staged and his guns were not truly interchangeable. What made the system work was the American armories' patient combination of precise gauges, machine tools that replaced skilled hand filing, and government money from the War Department, which valued standard weapons that soldiers could repair in the field. The earlier factory machines of the Industrial Revolution supplied the power and the example of organized machine production.¹

The method spread from guns to clocks, sewing machines, typewriters, farm machinery and bicycles through machinists who moved between firms, and was shown to the world at the Crystal Palace Exhibition of 1851, where Colt revolvers and Hobbs locks impressed British engineers. A British government commission visited American arms makers in 1854 and Britain bought American machinery for its Enfield armory. By the 1890s the same logic, parts that are made, not fitted, led to Ford's assembly line (1913) and the era of mass production.