The selector plate is a shifting part that adjusts the engagement between the cut off lever and sector gear relative to the fire selector switch on the automatic electric gun’s receiver.
When the fire selector switch is set to safe, often the selector plate is shifted so that the copper component is pushed away from bridging the contacts on the trigger switch contacts.
When the fire selector is set to semi, the selector plate is shifted to bridge the contacts on the trigger switch and engage the cut off lever to contact the cam on the sector gear’s axle limiting the current to a single cycle of the piston.
When the fire selector is set to auto, the copper contacts on the trigger switch are bridged again. This time, the position of the selector plate no longer applies pressure against the cut of lever allowing for continuous cycle.