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
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Examples from the Web for tuning key
Historical Examples of tuning key
But Czipra began to put the strings of the czimbalom out of tune with her tuning-key.
Debts of HonorMaurus Jkai
"That I could help," said Arnold, as he took his tuning-key out of his pocket.
They had strings of brass wire which were tuned by a key, not very different from the present tuning-key.
The Story of Ancient Irish CivilizationP. W. Joyce