This is the finger lever latch (also called the finger lever catch) Winchester 1873 2nd and 3rd model. It fits all 1876 model rifles. This part is located on the lower tang and catches the projection on the finger lever to keep it locked in place when not in use. It is held in by a pin (7027pin) and the finger lever latch spring (7027s) maintains tension. NOTE: there is an early finger lever latch that was used up to serial number 28,000 that is the same that was used on the model 1866. This one was threaded into the lower tang rather than pinned.