4. _The back check, hammer stem and regulating button_ are subject to
the same faults as their counterparts in the upright, which may be
remedied in the same way. Bridles and hammer springs are not needed in
the square, as the weight of the hammer, moving in a vertical
direction, is sufficient to bring it to its rest position.

5. _Hammers_, when made of felt, will of course require the same
treatment as those in the upright. In many old squares the hammers are
built up of buckskin. If this becomes beaten down hard, it is well to
cap the hammer with a new soft piece of buckskin, gluing only at the
back ends.

6. _Butts and Flanges_.--A click just as the key comes up, indicates
that the felt cushion, against which the jack rests, is worn out and
must be replaced.

In all square actions the center pin, in the butt, is held by friction
alone, but rarely gets loose; if it should be found loose, put in a
larger pin.

The flange, shown in the cut, is what is called a split flange. By the
set screw T, the jaws can be regulated so that they neither clamp
the center pin so tightly as to make the action sluggish nor so
loosely as to let the hammer wabble.

If the bushing cloth is found to be badly worn, it is better to put in
new, which must be done neatly, or the result will not be
satisfactory.