I am reading Nature's Metropolis by William Cronon (Norton, 1991). The central thesis of the book is that cities like Chicago are shaped by their outlying economies of farming, lumbering, and livestock and, in turn, the cities shape those outlying economies. It is a symbiotic relationship in which a city is not possible without the country around it or vice versa. But the book also brought up a related topic which intrigues me: interchangeability. We live in a world where interchangeability is so deeply ingrained in our culture that we don't even think about it. Need an oil change? Any service station will have a filter that fits your engine. Need to replace a light bulb? Every bulb is designed to fit a standard socket. What amazes us now are things that are not interchangeable. These are almost by definition hand-crafted and very expensive.
You might say that interchangeability dates all the way back to Johannes Gutenberg and his invention of moveable type. Any letter could, after all, be put in any position along a line of type. But the extension of that idea to other devices dates back more to 18th century France. A French artillery officer with the wonderful name of Lieutenant General Jean Baptiste Vaquette de Gribeauval came up with the idea of standardizing all of the parts in the French Army's canon inventory. His ideas were not fully implemented, but another Frenchman, Honore Blanc, actually began mass-producing muskets from interchangeable parts in 1790. Thomas Jefferson met Blanc while Jefferson was the United States Ambassador to the French Court. He communicated the idea back to the War Department because it would allow the production of a large quantity of weapons without having to have a large number of skilled gunsmiths. America just didn't have that many skilled craftsmen to meet the demand for a large order.
About this same time, Eli Whitney (yes, the same Eli Whitney of cotton gin fame) started to get interested in making rifles for the U.S. Government. It seemed a more lucrative business than the cotton gin which had more or less been stolen from him by patent pirates. Whitney came to Congress with a load of parts which he claimed were made identically and assembled rifles by randomly selecting parts from different barrels. The Congress was duly impressed and placed an order which Whitney took eight years to complete. The trouble was, Whitney's so-called interchangeable parts had all been carefully filed by skilled craftsmen to make them fit together but they were not truly produced to interchangeable tolerances. Others got into the game and the first truly interchangeable device built in America was a clock made by Eli Terry in 1816 from mass-produced wooden parts. There were others who rightfully deserve the credit for the first firearm made from interchangeable metal parts including John Hall and Simeon North.
A second example that came out of the book was standardized lumber dimensions. With the advent of lumber cut to dimensions such as 2 inches by 4 inches or 2 inches by 8 inches, building could now be put together almost like Erector Sets in what became known as balloon-frame construction (because the frame was so light compared to older post-and-beam construction). Standardization brings efficiency and efficiency brings economy. We could never afford all the modern conveniences that make up our world were it not for this pervasive idea of interchangeability. It is everywhere, not just machines. As long as something functions within a certain defined set of parameters, it can be substituted for something else that fits the same parameter space. If two things are not interchangeable, you know there is at least one parameter (which might even be an esthetic one) which is not the same.
Interchangeability was the power that allowed Gutenberg to revolutionize printing. Interchangeability remains one of the most powerful ideas in our modern world.