_A Tool for Fitting Hammers to Gun Locks._—The usual practice in fitting hammers to gun locks is to measure with the dividers the distance from the centre of the tumbler, where it projects beyond the lock-plate, to the centre of the tube or cone, and so get the length of the hammer; then drill the hole in the hammer, square this hole by the rule of “guess,” and file until it fits upon the square of the tumbler. [Illustration: FIGURE 49.] A simple tool can be made by any gunsmith, that will greatly facilitate his operations in fitting hammers. The accompanying cut (Fig. 49) shows this tool in full size. It is made of iron or steel, one-eighth of an inch thick. The body, A, of the tool is one-half inch wide, and has a slot, _a_, three-sixteenths of an inch wide and one inch long. The curved slot, _b_, is the same width, and embraces about one-fourth of a circle. The nose-piece, B, is shaped like the top portion of a hammer, and is held to the body, A, by a screw, _c_, and to insure its moving in a line, and being held properly in the slot, _a_, there is a small stud, _d_, that fills the slot. In the lower curved portion of the body, which is seven-eighths of an inch in diameter, there is a five-eighths hole, which receives the round portion of the piece, C. This piece has an extension, as shown by the dotted lines, and is held to A by a screw, _e_. The square hole in this piece is intended to fit the square of the tumbler of the lock. The thickness of C, at the round part where it enters A, is the thickness of both A and B. There is a shoulder of the thickness of B, and of the size of the body of the tool at the lower end, being of the same diameter, so that the back surfaces of B and C are of the same thickness. The front surface of C is flush with A. To use the tool, put the square of the lock tumbler in the square hole of C, and put the tumbler screw in place. Loosen the screw, _e_, and turn the piece, C, until the nose of B will rest pretty firmly on the gun-tube; then turn the screw to hold it in place. Loosen the screw, _c_, that holds B in place, and move this piece up or down until the centre of the nose rests squarely on the tube; then confine it in place by turning up the screw, _c_. This is now an exact pattern, giving the length, shape of the hammer, and also a guide to form the square where it fits the tumbler. It must be observed that the screws and the stud, _d_, ought to fill the slots on the shoulder of the piece, C, a good fit, so that it will turn evenly and properly in the hole of A. The screws may be the same that are used for tumbler screws for army muskets. These screws are hardened, and, as they have large flat heads, they answer for this purpose very well. The part, C, can be made of two pieces of the same thickness as the other parts. Finish them separately, except the square hole, and then solder or rivet them together. The square hole is best finished up when the two parts are fastened together.