4. Bridle and Bridle Wire.—­In putting in a new bridle, it should be doubled over at the end and secured to the hammer butt by a small tack.  Be sure you get it exactly the same length as the others; otherwise it will be necessary to bend the bridle wire out of line.  Some tuners glue the bridle around the back catch stem, but the above method is preferable.

The purpose of the bridle is to jerk the hammer back quickly and the wire must be set, neither so far back as to check the stroke of the hammer, nor so far forward that the bridle is too slack to draw upon the hammer.

5. Jack.—­The jack itself seldom gets out of order.  So long as its flange does not come unglued in the wippen, or its spring get out of place or broken, or get tight in its joint, it will need nothing.  Its adjustment and action is controlled by the bottom or capstan, and the regulating button.

6. Regulating Button.—­This button determines the point in the stroke of the hammer where the jack flies off from the nose of the butt.  If the button is too high, the jack does not fly off soon enough, and the result is, that the hammer either blocks against the string or bounces from the jack after the stroke has been made, striking the string a second or third time from one stroke of the key.  The felt punching on the lower side of the button often wears until this trouble prevails.  Lower the button by turning down the screw on top of the regulator rail; if lowered too far, however, the action is weakened by causing the jack to fly off too soon, without giving the hammer a sufficient impulse.  A regulating screwdriver is used for this, but in its absence, a wire hook, similar to a shoe buttoner, will turn the screw.

The block rail is properly adjusted at the factory and requires no attention.

7. Hammer Butt.—­The felts and leather on the heel of the hammer butt wear out and must be replaced.  The felt cushion, that is lowest and farthest to the left (see illustration), is the one that wears out first.  The jack, in returning to the notch, strikes this cushion, and in time wears it away so that the jack in returning strikes the wood of the hammer butt, producing a sharp click, which is very annoying, to say the least.  This click is heard at the instant the key rises to its rest position.  Sometimes, however, a similar click is produced by the top of the key striking the board which is set over the keys, due to the cloth being eaten off by moths, or a pencil or some other article lying on the keys back of this board.

The center pin in the butt of some cheap actions is not held in the butt by metal clip and screw, and if it gets loose so that it works out, must be replaced by a larger pin.  The size of center pins generally used in the factory, is .050 of an inch in diameter; the size for repairing should be .053.  All of the best actions have the set screw with which to make the pin fast in the butt.