For centuries, guns and other devices were made one at a time by gunsmiths, and each gun was unique. If one single weapon needed a replacement, it either had to be sent back to the original gunsmith or thrown away and replaced by another weapon.
Eli Whitney, who would later be the inventor of the cotton gin, saw great benefits in developing "interchangeable parts" for United States government equipment. Some time around 1798 Whitney built ten guns, all containing the same parts and mechanisms, and disassembled them before the United States Congress. He placed the parts in a large pile and, with help, reassembled all of the weapons right in front of the Congress.
The Congress was immensely impressed and ordered a standard for all United States equipment. With interchangeable parts, the problems that plagued the era of unique weapons and equipment had passed, and if one mechanism in a weapon failed, a new piece could be ordered and the weapon would not have to be discarded.
The principle of interchangeable parts made mass production relatively easy. It was based on the use of templates, applied by semi-skilled labor using machine tools instead of the traditional hand tools.
Eli Whitney's mechanical talents and enterprising nature led him to a revolutionary innovation; the manufacture of products with interchangeable parts became a key element in modern industrial production. Many consider this invention even more beneficiary than the cotton gin which he introduced five years later.