Tangentially to the axis, four brass fins bent twice, all in the same direction, are welded; since the frame slopes slightly towards the outlet of the tube in the form of a flute mouthpiece, a more or less strong jet of air strikes all the fins on their concave side, thus making them rotate.
The rotating shaft is made of steel, it is 12 cm long and at the extremities has two brass disks 4.2 cm in diameter, each with three holes for screwing onto them the disks that are to be rotated.