G P, is the guide pin, generally of oval shape, with the longest diameter in line with the key.  The hole in the lower portion of the key, in which the guide pin works, is bushed with bushing cloth and is made to fit so closely that the key will not move laterally, yet not so tightly that the key will not work easily.

Bm, is a wooden block called the bottom; sometimes called the key-rocker.  It is held in position by the two screws shown in cut by which it can be adjusted or regulated.

E, is the extension communicating the motion of the key to the upper part of the action.  There are various ways in which the extension is connected to the bottom.  In this action, the extension is made round at the lower end and fits snugly into a hole in the bottom upon a felt 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.

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.)