The part of the mouthpiece from the body to the back. Sometimes the bore of the shank is too small to go far enough on the neck to tune properly. Often this can be fixed by sanding the neck cork, but occasionally the best solution is to enlarge the back bore. This is relatively easy to do and has no noticeable effect on how a mouthpiece plays. The shank can also be made smaller to fit a smaller cork by filling with any hard, permanent material. This also has no effect on the sound.