Tuning Pegs (túnɪŋ pɛ́gz), or string adjusters, are the knobs that protrude out of the head of the guitar which are used to add or remove tension on the guitar. Tuning pegs use a gear system to move attached  cylinders called “tuning posts,” which is where the  strings are fastened to the head of the guitar. As the tuning post is turned, the tuning peg rotates which  either loosens or tightens the string.