Edison's most important invention.

In 1890,  10 years after the introduction of his longer-lasting light bulb, Thomas Edison came up with the idea of a screw-in socket.  Before that, asking "How many engineers does it take to screw in a light bulb?" would make no sense whatsoever.
This basic socket design outlived all other light bulb technologies. Even today, 120 years later, the latest and greatest LED lights are manufactured according to the standard based on Edison's original idea.

tags: invention, problem, interface, control point, system, patent