The bore of the soprano clarinet is cylindrical for most of the tube with an inner bore diameter between 14 and 15.5 millimetres (0.55 and 0.61 in), but there is a subtle hourglass shape, with the thinnest part below the junction between the upper and lower joint. The reduction is 1 to 3 millimetres (0.039 to 0.118 in) depending on the maker. This hourglass shape, although not visible to the naked eye, helps to correct the pitch/scale discrepancy between the chalumeau and clarino registers (perfect 12th).[19] 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 instrument flares out to improve the tone of the lowest notes.