Specifically manufactured cubes that fit between the breech face and hood of the barrel, for dry-fire practice.
Precisely determined width perfect for the distance the trigger on Glocks need to travel to reset. Unlike other, less precise, methods, the trigger movement is perfectly repeatable from shot to shot and calibrated to realistic live fire travel distances. No mushing of the trigger.
Because the cube only allows the trigger to move to the reset point there is greater chance of improving trigger control.
Ideal for practicing trigger speed or multiple shot drills in dry fire. It does not create a resetting trigger but rather is a sophisticated way of unlocking the gun enough that the trigger manipulates forwards and backwards without the striker falling.