Castanets are used in pairs. Traditionally two pairs are played together, one pair held in each hand. There is a string which passes through small holes in the shells. The player winds the string around the thumb and finger so that the two shells can be clicked together. The two pairs of castanets used are slightly different sizes so that they make a slightly different pitch. The higher pair, known as "hembra" (female), is usually held in the right hand, with the larger "macho" (male) pair held in the left.