Holds an additional 3 – 2.75 inch shotgun shells. Constructed of Military Type III anodized, 6061 T6 aluminum. Virtually indestructible. Minimum barrel length of 20 inches. Includes magazine spring. Easy installation. Ratchet base for tight fit. New fluted design. Includes swivel stud cap. Outside diameter of the extension is engineered to match the diameter of the shotgun barrel lug. Manufactured in the USA.