For any quarter inch jack, this is a set of 2 nylon washers, one of which has has an inside ridge to keep the jack from touching the metal enclosure. One washer goes on the outside of the enclosure and the other on the inside. This is for applications where you want the jack to be free from the ground plane of the enclosure itself. This is good for:
- Ground isolation for output jacks after transformer isolation
- Control output to an expression pedal,
- Output to a foot switch control (such as "Tails" on an echo or reverb stompbox)
- Attaching another box with more circuitry (such as a diode clipper switch box)
- The possibilities are limitless and only bound by your own imagination!
The hole size needed is 1/2 inch hole to accommodate the insulator (normal hole size for a quarter inch jack is 3/8 inch).