_M R_, is the main rail; so called because the main constituents of
the action are attached to it. (Everything designated as "rail" in the
action runs the entire length of the 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