tuning key

noun

a device that may be placed over a wrest pin on a piano, etc, and turned to alter the tension and pitch of a string
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

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