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 the "back catch" (the backward projection of the
butt), at a short distance from the string in its return, and prevent
the hammer from falling entirely back to its rest position, thereby
preventing quick repetition.

_Bl_, bridle. This is a piece of tape about an eighth of an inch wide
with a piece of leather glued to the end and a hole near the end for
the point of the "stirrup" or bridle wire. The cut shows where the
bridle is fastened in the hammer butt by being put into the hole in
the butt, and the back catch stem covered with glue and driven in by
it which precludes all possibility of its coming loose. The bridle
passes through a hole in the lower part of the back catch. Its purpose
is to assist the hammer to return quickly by hanging to it with the