In such instruments as the organ, accordion, piano or harpsichord a key is a balanced lever which when depressed by the finger either operates a valve to admit air to a pipe or reed, or mechanically energizes (strikes or plucks) a tuned string.
In mouth-blown instruments it is a mechanical device which governs a tone-hole that is out of reach of, or too large for, the unaided finger. It has three elements, a padded plate or cup to close the hole, a pivoted lever, or shank, and a touchpiece for the finger. This touchpiece may be a ring surrounding a directly fingered hole. Keys when at rest may be either open or closed, and two or more simple levers may be combined to form one key. On brass instruments there may also be a water key to release trapped moisture.
See Keywork.
PHILIP BATE