The elbow is the peice that connects the hopper to the gun itself. Guns that have a verticle feed tube don't need it, as the hopper will fit right on, but the guns that have that cocked to the side kind of feed tube (I can't remember right now the official term for it), require an elbow for the hopper to fit on and sit vertical, not directly over the gun but off to the side. The better ones habe thumbscrews at each end to let you adjust to different feed tube and hopper neck sizes. They run pretty cheap, $1/$2 at most fields.