There was a story I recall reading back in high school about Whitney. In it he demonstrated the concept of interchangeable parts to athe then President and the War Department by having thempick up any part from a group of parts piles and assemble several rifles. When they assembles them, the rifles all worked, demonstrating the superiority of mass produced parts over one off, blacksmith produced, parts.

Supposedly, that was the beginning of that phase of the industrial revolution.