The Airbrush Needle Spring is an important component part of the airbrush needle assembly that allows the needle to trigger back and forth smoothly through the airbrush nozzle tip, so that the liquid makeup flows properly. Without this spring your airbrush trigger will not operate the needle movement. This is a precision manufactured part specifically designed for the "Mist"ique Airbrushes and needles, and made of a strong, durable metal alloy. These little springs 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!