I was working on a 60's Fender Coronado semi-hollow archtop, and thought it would make an interesting guitar repair article...Factory finished in ultra-ugly green streaks over a natural top...so nasty it's cool! It had the typical crackling volume and tone pots (potentiometers) when plugged in, so they needed to be cleaned. This is normally no big deal, you simply spray some contact cleaner into the pot's opening between the leads. This is easliy done when the pots are mounted to a removable pickguard, or when there's a rear-routed control cavity, but on f-hole instruments, it can be a challenge and risk to loosen the nuts and move them to the f-hole's edge for cleaning.
The problem with this seemingly simple repair is this: The solder points, capacitors, and wiring can often be fragile and brittle. Trying to take the pots out can damage the precious vintage electronics. (Especially on an f-hole instrument where removal is often a tough job.) The finish can be scratched while trying to pull the pot through the hole, solvent can leak onto a label, etc...A simple pot cleaning can damage these sensitive elements, then your guitar has been forever devalued!
I use these really cool little tools that thread over the OUTSIDE of the pot, and connect to a can of cleaner! You simply thread the cylindrical housing of the tool down over the extended thread, connect the hose, and shoot the solvent in...no mess, no damage, and perfectly clean quiet pots! Even in rare cases where the threads don't match, or there isn't enough thread to screw it on, an o-ring over the pot shaft provides a seal, and it is still an easy job to hold the housing firmly down while injecting the solvent. This also keeps solvent from being sprayed sloppily into an f-hole HOPING that it gets in the pot...Yes folks, people do that believe it or not. These cool little units deliver a zero-risk venture on valuable, vintage instruments.