disc. When the action is taken out, the extensions simply lift out of
the holes, and when it is put back it is necessary to enter each one
in its place. In other actions, the upper side of the bottom where
the extension rests has no hole but simply a felt covering upon which
the extension rests; in this case it is necessary to provide what is
called an extension guide which is hinged to the extension guide rail
shown in the cut at the left of the extension. In actions of this
kind, the extensions remain in place at all times and the trouble of
placing them properly on the bottom when replacing the action is
obviated. Other methods also are employed which are readily understood
upon slight examination, but are essentially similar to the above.
Instead of the bottom, a capstan screw is used in some actions as
follows:

_Cpn_, is a capstan screw used in some actions in place of the bottom.
It is turned by inserting a pointed instrument in one of the four
holes, thus raising or lowering the capstan in regulating. The lower
end of the extension is felted. In such actions the extension is
invariably provided with the extension guide.

_B_, is the metal action bracket. The bracket is one solid piece of
metal. There are generally four brackets in the upright action. The
brackets rest on supports in and at the sides of the keybed, and are
secured at the top by large bolts,

_BB_, which go through the metal plate and into the wooden frame or
pin block. At the top of each bracket is an opening to receive this
bolt and a thumbscrew (not shown in the cut, being behind the hammer)
which fastens the action securely in position.