_L_, is the lead put in this portion of the key to balance it, and to
insure uniformity of "touch," and quick and certain return of key to
its rest position. As there is more or less difference in the length
of keys, and also in the weight of the hammers operated by them, some
keys are leaded much more heavily than others. In some cases the lead
is inserted in the extreme back end of the key; in others it is put
near the balance rail according to the requirement. In some actions
the lead is omitted entirely; but in the best actions it is almost
invariably present. In the action of the grand piano the keys are
leaded in front of the balance rail instead of back of it. This is due
to the fact that in the grand piano the hammer rests in a horizontal
position and its whole weight must be actually lifted and the force of
gravity overcome, while in the upright, the hammer rests in a
vertical position, only requiring to be thrown forward.

_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