This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
In connecting a small 1/8 -hp. motor to a small air pump where both shafts were % in. in diameter, I quickly made a coupling that would save the wear on the machines, as follows. The coupling was made of a piece of 3/4-in. brass rod with a 3/8 -in. hole drilled through its center. One end of the hole was enlarged to 7-16 in. for about 7/8 in. The end of the coupling having the small hole was slipped on the pump shaft and fastened with two setscrews. The other end was drilled to take a pin loosely, the pin fitting tightly in a hole drilled in the motor shaft. The pin was bent at one end so as to keep it from falling out and the other end fitted with two nuts. The motor shaft being a little loose in the coupling, gave it a chance to work free without binding. - Contributed by Leo J. Werner, New York City.
Ill: Coupling on the Shafts