The bore is cylindrical for most of the tube with an inner bore diameter between , but there is a subtle hourglass shape, with the thinnest part below the junction between the upper and lower joint. The reduction is depending on the maker. This hourglass shape, although invisible to the naked eye, helps to correct the pitch/scale discrepancy between the chalumeau and clarion registers (perfect twelfth). The diameter of the bore affects characteristics such as available harmonics, timbre, and pitch stability (how far the player can bend a note in the manner required in jazz and other music). The bell at the bottom of the clarinet flares out to improve the tone and tuning of the lowest notes.