action in one solid piece.)

_W_, is the wippen. Those pieces upon which or by which the small
letter _g_ is shown are the flanges. The one at the left of the wippen
is called the wippen flange. It is made fast to the main rail by a
screw, and upon it the wippen is hinged by means of a "center-pin" at
the lower end. The center-pin in the wippen is driven through a hole
in which it fits tightly and immovably in the middle part, and it (the
center-pin) is consequently stationary in the wippen. The flange
extends down at the sides of the wippen and the holes in flange are
made large enough to receive bushing cloth in which the center-pin
works freely but not loosely. All flange joints are of this nature;
some, however, are provided with a means for tightening the center-pin
in the middle portion of the joint.

_j_, is the jack. The purpose of the jack is to communicate the motion
of the wippen to the hammer. The precise adjustment of the jack and
the adjacent parts upon which it depends for its exact movements, play
an important part in regulating the "touch" of the piano, and will be
fully entered into in following lessons.

_js_, jack spring. Its purpose is to hold the jack inward against the
"nose" or "heel" of the hammer butt. (See _Bt_, hammer butt.)

_Rr_, regulating rail. The _regulating button_ is shown attached to
the rail by the regulating screw which is turned by means of its ring
on top of _Rr_. The purpose of the regulating button is to throw the
point of the jack out of the nose of the hammer butt, and allow the
hammer to rebound from the string. If the button is too high, it does
not throw or trip the jack in time to prevent blocking. When the
button is too low, it disengages too soon, and much of the force of
the key is lost before it reaches the hammer.

_BR_, is the block rail, felted on the side next to the jack which
strikes against it when thrown from nose. This rail is absent in some
actions, in which case the back of the jack is felted and strikes
against the "back catch," which is also felted on inner side. (The
back catch has no mark in the cut, but is explained below in
connection with the "back check.")

_BC_, is the back check which is simply a piece of wood with a thick
piece of felt glued to the inner face and suspended on a wire.

_BCW_, back check wire supporting the back check, and screwed to the
wippen. The purpose of the back check is to check the hammer by coming
in contact with