Having spare parts on hand when you need them is a diver's motto. A spare Gun Butt can assure you always come home with game. Don t let the lack of spares skunk you on your next hunt, always carry spares. The JBL Deluxe Gun Butt is designed for JBL Magnum Series of Spear Guns that are equipped with a 1-1/4 Aluminum Barrels. Gun Butt is made from durable non corrosive plastic and is easy to install. Gun Butt makes a great save a dive kit item.