I did not invent this but i did modify the idea I learned from a youtube video. I used one of my slim helicopter rails made of carbon fiber , buy you can use any smooth rod like object that will fit inside the propeller hub.the the gas line tubing fits I went to my fav hobby shop and picked up an inch of used standard fuel line clear tubing.(free) The tubing fits snugly into the opening of the self tightening screws hub. I used my rail as my balancing rod. The tubing fits perfectly over the railing end. You can use any straight smooth rod that fits the tubing then i stick the tubing end into the hub and use a soup bowl to balance the rod on. you can use any glass or smooth flat surface. Place the bowl on level table ( use a level to make sure the table is levell in all directions..and hang the prop with the rod inside over the side. the side of the prop that is lower when balancing is the heavier side and needs some light sanding to achieve perfect balancing after sanding the heavier side, redo the balance test until both sides seem the same height. I put one layer of electrical tape over the tubing to make a tighter fit and keeps the tubing centered. Cost 0.00, (one layer tape, one inch of tubing , I was given used tubing by the shop I already had the rail ,that happened to fit the job and the soup bowl that was in my kitchen. Try it, it works very well.