I remember watching a documentary about a country in central Africa where, less than 15 years ago, blacksmiths were making screws and nuts by hand. They needed

I remember watching a documentary about a country in central Africa where, less than 15 years ago, blacksmiths were making screws and nuts by hand. They needed to be kept together or the manufacturing variations would mean that last week's screws might not fit this week's nuts. These guys were fast, but nowhere remotely as fast as thread-rolling machinery of course.