$3 鄧槳器

材料:

1) Neodym magnet $2

2) 3mm, 4mm screw, spacer and nut

screw must cut to cone on both side, can use a dremel.

The magnet can hold the prop and screw in air and rotate freely.

Very accurate! I can use it to balance all my 325mm carbon blade , 515mm carbon blades, 58mm tail balde