Our original guitar BackAxe, adjusts to fit any size or shape acoustic or electric guitar case--square or contoured. It allows you to carry your instrument protected in its hard-shell case with the convenience of a backpack. It will also adjust to fit a banjo, electric bass and many other cases of similar size. Once adjusted (click the directions button on the left to see) you simply flip it over your case and close the 2 side-release buckles to get it on. You'll use it any time you carry your axe anywhere.