The Airbrush Auxiliary /Back Lever is an important component part of the airbrush needle assembly in which the trigger button opens the airflow and allows the needle to trigger back and forth smoothly through the airbrush nozzle tip, so that the liquid makeup flows properly. Without this back lever your airbrush trigger will not operate the air valve and needle movement correctly. The back lever works with the needle assembly spring to push the trigger forward, when the trigger is released, thereby closing off the air and makeup flow. This is a precision manufactured part specifically designed for the "Mist"ique Airbrushes and needles, and made of a strong, durable metal alloy. These back levers have a way of getting lost when taking an airbrush apart, so it's best to keep an extra on hand. Your airbrush will not function properly without it!