 Manufacturers produce reeds in different strengths, indicated by a number (most commonly 2, 2.5, 3, 3.5, 4, 4.5, and 5).The strength is determined by a machine in the reed-making process that presses against the vamp (the part of the reed that includes the tip, where the tongue is placed, and the heart just behind the tip) of the reed and determines how stiff the reed is.The machines separates the reeds according to strength.