[Rangi42]

Richard Feynman mentions these in Surely You're Joking, Mr. Feynman!:

> One mechanical engineer at Frankfort was always trying to design things and could never get everything right. One time he designed a box full of gears, one of which was a big, eight-inch-diameter gear wheel that had six spokes. The fella says excitedly “Well, boss, how is it? How is it?”

> “Just fine!” the boss replies. “All you have to do is specify a shaft passer on each of the spokes, so the gear wheel can turn!” The guy had designed a shaft that went right between the spokes!

> The boss went on to tell us that there was such a thing as a shaft passer (I thought he must have been joking). It was invented by the Germans during the war to keep the British minesweepers from catching the cables that held the German mines floating under water at a certain depth. With these shaft passers, the German cables could allow the British cables to pass through as if they were going through a revolving door. So it was possible to put shaft passers on all the spokes, but the boss didn’t mean that the machinists should go to all that trouble; the guy should instead just redesign it and put the shaft somewhere else.