ToneShapers Kit, Internal Tooth Lock Washer, 3/8" Thin (12)

I bought a single pack of these to see if they would work well/fit on input/output jacks on my DIY pedals. They do.
Previously, the nuts on the jacks would become loose after plugging in/unplugging cables over time. The catch was always that there isn't much space on the threaded portion of the jack to fit a washer in between the jack and the inside of the case. These locking washers take up almost no space, yet hold the jack in place.