Machine head

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A machine head (also referred to as a tuning machine, tuner, or gear head) is a geared apparatus for tuning stringed musical instruments by adjusting string tension. Machine heads are used on mandolins, guitars, double basses and others, and are usually located on the instrument's headstock. Other names for guitar tuners include pegs, gears, machines, cranks, knobs, tensioners and tighteners.

Non-geared tuning devices as used on violins, violas, cellos, lutes, older Flamenco guitars and ukuleles are known as friction pegs, which hold the string to tension by way of friction caused by their tapered shape and by the string pull created by the tight string.