_How to Put up a Lock._—In taking down the lock the last thing removed was the sear-spring, perhaps—it is most convenient to make that the last thing. Now, in putting up the lock, that is the first part to claim our attention. Screw the sear-spring into position, then the sear; next put in the tumbler, and then put on the bridle. Having this all right, screw on the hammer and let it down. Then take the mainspring, clamped as it was at the taking down, hook it on to the swivel, and bring it up until the little steady-pin is in its hole in the plate. Now unscrew the vise and the lock is ready for work. It will be necessary to always handle the mainspring with care. It is the first thing to come off in taking down, and the last to go on in putting up the lock; and the vise or clamp must be turned upon it only just enough to bring it loose, and no more. If more, it may be damaged, possibly broken. Handling the parts of a lock with chamois skin or paper, is a good idea, while brushing off the chalk and rubbing them clean with the brush, and it is also a good idea not to touch them with the naked fingers afterwards. Few gunsmiths would be inclined to take this precaution, but it is worthy of consideration if one desires to be ranked among the very best and most careful of workmen; as handling with the naked fingers is apt to leave the parts in such a condition as will cause them to eventually rust, slightly at least. CHAPTER XXIII. ON FITTING GUN HAMMERS. _To Fit a Hammer on a Tumbler._—To file the hole in a gun-hammer so that it will rest firmly and evenly upon the squared end of the tumbler, has tested the skill and patience of nearly every gunsmith. The usual practice is to drill a hole nearly the diameter of the square of the tumbler, then file this hole until it fits the square, and unless skill and patience are brought into requisition, and a nice fit be the result, the hammer soon works loose, then needs refitting. The remedy then generally is, remove the hammer from the tumbler and close the hole a little by cutting around the squared opening, a little distance back from the edge, with a sharp cold chisel, thus throwing some of the metal inward, closing the hole a trifle. The hammer is then put upon the tumbler, and if it be a little tight is driven to place with a hammer. After some usage it becomes loose again, and has to be again refitted. It is evident that unless what might be called a “perfect fit” be made, that the sudden arrest of the hammer upon the tube or cone, as it descends by force of the mainspring, will cause some slight displacement of metal where the hammer and tumbler come in juxtaposition. A repetition of these sudden arrests increases the displacement, and often there is considerable looseness of the parts. [Illustration: FIGURE 48.]