The Rocky Mountain Bully Bull Extreme Elk Grunt Tube is designed to be used with a mouth call diaphragm. It creates an even flow of air for back pressure. This makes it easier to obtain octave note changes. Bully Bull includes camo cover and lanyard. The mouth opening is 1 1/2 inches and the length is 21 3/8 inches. Buy yours today at Sawyer's Country Edge.