noun
tuning peg; tuning pin
Specifically the peg on a shamisen or similar Japanese stringed instrument used to adjust string tension and pitch.
三味線の音締めを回して調弦する。
I tune the shamisen by turning the tuning pegs.
糸巻き is a more general term for tuning pegs on various stringed instruments, while 音締め is strongly associated with the shamisen.
Compound of 音 (ne, 'sound') and 締め (shime, 'tightening'), referring to the peg that tightens the string to adjust the sound.