Back when I was first assembling our panel and wiring everything up, I had a hard time finding non-conductive shoulder washers for our two 3.5mm “earbud” size audio jacks. The big 1/4″ jacks had washers like these to isolate them from the airframe ground, but not the little guys. Well, this was a case of too much thinking and not enough information. I recently replaced our Flightcom 403b intercom with a PSEngineering PM3000 to better handle the high cabin noise level, and while rewiring much of the audio system, I learned that these little jacks are already set up for this. Look closely at this picture:
Notice that just under the silver part is a little black plastic shoulder. The way this is supposed to work is that we are to drill a hole in the panel that is the same diameter as that black shoulder part, not the silver threaded part. Then, we just need a flat non-conductive washer that will isolate the nut from the panel. I made my own out of an old hotel room key. Wasn’t that easy?