Alum. spinner balance
Isacc F....Unless you find the back-plate is out of balance...leave it alone. It should be fine. If it is out of balance...drill small holes in the back of the back-plate...out towards the edge...to make it perfect. (you don't have to drill them all the way through)
If the spinner is out of balance....(the assy.) or if you had to enlarge the cone for the prop to fit...you will have to re-balance.
With a felt-tip marker...mark the place on the front of the back-plate where the opening for the prop fits (using the cone).
Mark also the cone...so that it goes back together the same way.
Any metal that needs to be removed ...will be cut from the prop opening on "the heavy Side".
With a little patientence...even a spinner that had to be "opened up"...can be brought back into perfect balance.
Here's a pic of a typical cut...I hope this helps....Dave...
And another pic of the "re-assembly marks".