Each of the small pegs on the head of a guitar, used for tightening the strings.
吉他弦轴（位于吉他顶部，共有两个，用于绷紧琴弦）
Example sentencesExamples
From then onwards all tuning takes place down at the bridge using the fine tuners (I've not used the regular machine heads yet - the guitar just stays in tune).
He'd carefully scrubbed the machine heads and pick-ups with the detachable head of a burnt-out electric toothbrush, and wiped the sweat and dust from each string until they gleamed packet-fresh.
And his Sitardata, molded on the Indian sitar, is a stainless steel bowl with machine heads and a metal bar.
They do not necessarily need to be in tune - the machine heads on the modern bass are basically only there for effect - nails will serve just as well.