Knob Position Indicator

These are handy little pieces for other than their design purpose.
I personally don't like soldering to the back of pots. Instead, take one of these, flatten the pointer and solder a lead to it. Put it on the shaft first then install the pot. Run the lead to a common grounding point and avoid the possibility of damaging the pot by overheating it.
They also are wonderful as a common ground point. Drill a hole for a small screw into the flat, bend the ring to 90 degrees and screw the thing to the inside wall of the electronics hollow. Presto, common ground point.

Why have numbers on your knobs if you can only guess +/- 3 of where they're set? I use the tone controls on my dual humbucker instruments a lot-- There's a profound difference in sound between 2 and 4 where there's less roll-off between say 6 and 10. These simple little pointers make it much easier for me to dial-in 2.5 or 3 rather than have to blindly tweak the control in search of the sound I want. Their edges are polished nicely and they're shiny, but they are just stamped sheet metal, so their looks may not appeal to everyone.