Momentary kill switch. S.P.S.T. normally-closed, momentary push-button. Press to use, release to return. 0.51" diameter red plunger, 0.74" diameter metal bezel. 0.62" diameter threaded bushing mounts in panels up to 0.15" thick. Solder lug terminals attached.
Regardless of the instrument's electronics configuration, this switch should be wired in just before the jack; it will become the second-to-last electronic part in the progression of components.