Beginning with the key, it has its balance pin, guide pin, cushions,
etc., practically the same as in the other types.

The bottom, or key rocker, is reversed in the square; the end
transmitting the motion being nearest the performer.

The extension and wippen are absent in the square, as the jack is
attached directly to the bottom or key-rocker.

The back check is screwed to the key, and as the hammer head rests
against it after striking, the use of the contrivance called the back
catch in the upright is unnecessary.

[Illustration: ACTION OF THE SQUARE PIANO.]

ACTION OF THE SQUARE PIANO.

A. Action Frame.

B's Indicate the Cushions, or Bushing, of felt, cloth or leather.

C. Balance Rail.

D. Balance Pin. Round.

E. Mortised Cap for Balance Pin. Bushed.

F. Key.