Some C trumpets have tuning issues that require the use of alternate fingerings. Common examples of this are a flat 4th space E or 4th line D. Many C trumpets with these tuning issues can be improved by using a shorter shank screwed on to a normal upper backbore component. This will often improve the tuning of problem notes and improve slotting in general. Some Eb, D, and piccolo trumpets also work better with short shanks. Choose the size to match the upper backbore section, either S, M, ML, or L.