By rubbing the small stick over the notches of the Hui Machine you can make the propeller rotate. If you know the trick, you can make the propeller turn left or right (each change of direction is accompanied by the exclamation "Hui!"). If skillfully performed, the trick is not recognizable to the uninformed. Thus, the Hui machine is good for animation and fun at any party.

I know this toy already since the early 80s, at that time of course made of wood, and I have made dozens of Hui myself.

If you want to know how the trick works: https://de.wikipedia.org/wiki/Hui-Maschine

For mounting the propeller you need a screw M3, length fits from 8 mm to 25 mm. I had 10 mm on hand.

If you have no screw, you can use the nail, that is included in the stl file. But a screw is working better.