_Nomenclature of the Gun Lock._—The number of pieces in a common gun lock, as shown, are thirteen, and are fully illustrated in the cut, Fig. 77. _A_, is the lock-plate; _B_, the hammer; _C_, mainspring; _D_, the bridle; _E_, the tumbler; _F_, the sear; _G_, the sear-spring; _H_, the swivel or stirrup; _I_, the sear-spring screw; _K_, _K_, _K_, the bridle screws; _L_, hole for side-screw. In some locks there are only two bridle screws. In others a screw holds the mainspring to place instead of a lip catching under the stud. [Illustration: FIGURE 80.] [Illustration: FIGURE 81.] _Nomenclature of the Hammer._—The names of different parts of the hammer, Fig. 78, are: _a_, the body; _b_, the head; _c_, the comb; _d_, the nose; _e_, the cup; _f_, tumbler-hole. [Illustration: FIGURE 82.] _Nomenclature of the Lock-Plate._—The names of different portions of the lock-plate, Fig. 79, are: _a_, the bolster; _b_, mainspring-catch; _c_, hole for mainspring-pivot; _d_, hole for side-screw; _e_, hole for arbor of tumbler; _f_, hole for sear-screw; _g_, hole for sear spring-screw; _h_, slot for sear-spring stud; _i_, _i_, holes for bridle screws. [Illustration: FIGURE 83.] [Illustration: FIGURE 84.] _Nomenclature of the Tumbler._—The names of the tumbler, Fig. 80, are: _a_, the body; _b_, arbor; _c_, squares; _d_, pivot; _e_, swivel arm; _f_, pin-hole, and _g_, the tumbler-screw hole. _Nomenclature of the Bridle._—The bridle, Fig. 81, consists of: _a_, the body; _b_, the eye for tumbler-pivot; _c_, hole for sear-screw; _d_, _d_, holes for bridle screws. Some tumblers have a pin that goes in a hole in the lock-plate, and this pin is called a pivot. [Illustration: FIGURE 85.] _Nomenclature of the Mainspring._—The mainspring, Fig. 82, consists of: _a_, the upper branch; _b_, the lower branch; _c_, the hook; _d_, the pivot; _e_, the catch which is sometimes called the tang. [Illustration: FIGURE 86.] _Nomenclature of the Sear._—The sear, Fig. 83, consists of: _a_, the body; _b_, the nose; _c_, the arm; _d_, screw-hole. _Nomenclature of the Sear-Spring._—The sear-spring, Fig. 84, consists of: _a_, the blade; _b_, upper branch; _c_, lower branch; _d_, the stud; _e_, screw-hole. _Nomenclature of the Swivel._—The mainspring-swivel or stirrup, Fig. 85, consists of: _a_, the body; _b_, the axis; and _c_, the tumbler-pin hole. _Nomenclature of the Breech-Pin._—Fig. 86 shows full size of musket-barrel breech-pin. _a_, plug with threads; _b_, tenon; _c_, tang; _d_, tang-screw hole; _e_, face. In sporting guns the tang is often called the “strap,” and is distinguished as long and short. The length varying from two and a half inches as shortest, and five inches as the longest. Sometimes the term “tail” is employed instead of tang or strap. The diameter of the plug is generally one-half, five-eighths, and three-quarters of an inch. The diameter of the pin used in United States muskets and rifles is three-quarters of an inch.