Thumb Stopper. New very effective guitar practice tool. Thumb stopper assists a guitar student in the proper placement of the thumb on the back of the guitar neck. Thumb stopper helps solve one of the most common problems among beginning guitarists - incorrect left hand position. Thumb stopper keeps your left thumb in the right place even when you're focusing on other things like sight-reading, or when your teacher is not around to correct you. It makes the learning process FASTER and EASIER! MUST HAVE FOR BEGINNERS.