Upright piano action: upright piano internal operation.
Felt: cloth surrounding the hammer.
Hammer: piece that hits the string to make it vibrate.
Hammer rail: hammer support when it is not operated.
Catcher: piece that catches the hammer tail when it falls.
Back check: piece that catches the hammer tail when it falls.
Key: part of the keyboard that is pressed to produce a note.
Wippen: piece to which the strings are attached and that transmits the sound to the soundboard.
Jack: piece that sends the hammer head towards the string.
Hammer butt: part of the hammer that is pushed by the jack.
Spring rail: support for the damper when it is not operated.
Damper: piece that prevents the string from vibrating.
String: part of the piano that produces the sound by vibration when hit.