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As with any technical subject, pianos have their own set of terminology. The following definitions may help you understand what your piano technician is telling you about your piano. You may also wish to see a diagram of the vertical action and the grand action.
action - mechanical part of the piano with moving parts. The top action refers to the removable assembly containing the hammers and wippens
agraffe - brass guide which serves as a termination point for unison strings toward the front of the piano
backcheck - leather or felt covered block which restricts hammer return movement from bouncing around so that notes can be repeated more quickly
bridge - long, narrow wooden piece which connects the strings to the sound board
bridge pin - metal pin in the top of the bridge which aligns the string
bushing - felt insert which touches the moving parts of the action
capstan - threaded rod or dowel fastened to the back end of a key to adjust the height of contact with the wippen
case - wooden cabinet which contains the piano's playing mechanism
console - upright piano 40" to 43" tall
damper - shaped felt which stops the vibration of a string when the key and damper pedal are released
damper pedal - (sustain pedal) pedal on the right which raises all the dampers
drop screw - small screw attached to the hammer flange which stops the upward motion of the repetition lever
duplex scaling - design which allows non-speaking portion of the string to vibrate sympathetically
fallboard - (keyboard cover) part of the case that closes to protect the keys
flange - hinge which allows another component such as a hammer or a wippen to rotate around a center pin
full upright piano - piano over 48" tall also known as upright grand
grand piano - piano with horizontal strings and soundboard
hammer - felt-covered mallet which is attached to the action by a hammer shank and is driven towards the strings to make sound
hitch pin - metal pin which anchors the end of the string opposite from the tuning pin
jack - action part which moves the hammer towards the string
key - wooden lever that pivots on a balance rail to raise the wippen via the capstan
keybed - part which supports the keyframe and keyboard
keyframe - wooden frame supporting the keyboard and action
keytop - ivory or synthetic covering for the keys
key bushing - felt insert near the key front or at the balance rail to minimize friction and unnecessary play
let-off - (escapement) part of the action causing the jack to rotate out from the hammer and facilitate repetition
music desk - part of case which holds the music
pinblock - multi-layered block of hardwood which anchors the tuning pins
plate - cast iron frame which supports the tension of the strings
regulation - process of adjusting the action to optimize touch and response
repetition - ability to play successive notes rapidly
sostenuto pedal - middle pedal which raises the dampers on the bass notes
soundboard - wood panel which covers the area under the strings and transmits sound outside the piano
spinet - upright piano under 40" tall with indirect or drop action
spoon - bent metal support attached to the wippen which supports the jack
string - steel wire of various diameters which is wrapped for bass strings or left bare for treble strings
studio upright - upright piano 44" to 48" tall
tuning - adjusting the pitch of all piano strings to arrive at an equal temperament scale
tuning pin - (wrest pin) threaded steel peg around which the piano wire is coiled
una corda pedal - leftmost pedal which shifts the action to the right so the hammers strike only one string
voicing - process of modifying the density of the hammer felts in order to reach optimal tone
wippen - transmits motion from the key to the hammer in such a way as to facilitate repetition of the key