The size of these reamers must be to suit the taps; that is they must be of a size corresponding to the tap if the thread were removed. The length of the extension may be about an inch, and the cutting portion of a length to correspond to the length of the breech-pins, for when using them where the reamer has entered the barrel until it is flush or even with the length of the cutting part, it is evident that it has penetrated as far as it ought to go. Be careful to keep the reamer well oiled when using it to ream out a breech. In making these reamers, turn them to the size and shape, and then file four spiral flutes, equi-distant from each other, with a small round file, but remember to file them “right hand,” like a right hand screw thread. About a quarter’s turn in the length is sufficient. The end where the cutting is done must be “cut back” between each flute, so as to make a cutting edge, or lip. The flutes serve to carry the chips away from the work, and prevent clogging. Above the end of the cutting portion, the reamer may be turned down to a size a little larger than the extension, and it will be then a very easy matter to nicely cut the flutes with a round file, as directed. _Breeching Taps._—The usual diameters of rifle breech pins are three-eighths, one-half, and five-eighths of an inch; of shot guns three-quarters and seven-eighths of an inch. The thread of the rifle is generally fourteen to the inch, and the shot gun sixteen to the inch. The breech pins of military arms vary. Some are made with coarse thread and some with fine thread, ranging from ten to eighteen threads per inch. There is no arbitrary rule for breeching guns, and excepting English made guns, almost every conceivable size and thread may be found in guns that are brought in to be repaired. In rifle and shot guns the fourteen and sixteen thread will be found to predominate. In unbreeching guns that have been made by “experts” of some country town, who built the arms “to order,” or in overhauling guns that have been repaired at the same kind of establishments, it will not be uncommon to find threads in the barrels that have been cut with a blacksmith’s taper tap, and the pin tapered to suit the thread so formed. It will be nothing uncommon to find a breech that is made to one side of the bore, or made with a crooked thread. If tapped with the taper tap, the thread may be found to be ten or twelve to the inch, according as a tap to fit the breech could be found. Let the workman discard all such ways of breeching guns. Let him procure a set of taps of the sizes and threads as noticed at the beginning of this article, and “stick to these sizes.” If the thread in a gun be worn, and the pin be loose or leak fire, then ream out the old thread, cut it anew, and put in a new pin. [Illustration: FIGURE 36.]