Items included are: Mount Plate and seven piece flow balls 1/8″ 3/16″ 1/4″ 5/16″ 3/8″ 7/16″ 1/2″. Flow balls or flow interrupters are used to upset airflow positively or negatively, to check corner radius, flow separation, dead areas, improve flow by reattachment and more. This listing is for the complete flow ball set and mount plate.