Hmmmm The store-bought balancers have tapered prop holders. That feature allows you to properly balance props of varying hole thicknesses. You just slide the tapered holders towards one another.

I couldn't tell if your invention ( pretty neat! ) had tapered holders. If not, it would easy enough to drill a hole in the center of a dowel; slide a bolt and nut into the hole; and chuck it into a drill or a drill press. Then, one could sand/file/cut a taper onto two of them. regards, Rich