This is the tang screw (also called the stock bolt) which attaches the stock to the gun. This screw goes down through the upper tang behind the hammer, through the wood stock and threads into the lower tang.This screw fits 1866 (late), 1892, 1894, 1895 and 1873 Lever action Winchester. It is straight grip receivers on all models except the 1873 uses this tang screw straight and pistol grip variations. This also fits Sears model 54 lever action.