Includes:Element Silent Piston Head and Element Silent Cylinder Head. The silent head set is an excellent upgrade for airsoft AEG's. The Element Silent head Set significantly reduces air leaks and gearbox noise. Professional installation of this product is highly recommended. Airsoft Station offers installation of most parts by professional airsmith technicians. For inquiries regarding installation of replacement and upgrade parts as well as other airsoft services please contact the Airsoft Station Tech Department here.