This is the screw that attaches the Spring brass trap door on the buttplate of the Winchester 1866, 1876 and 1873 lever action rifles. The compartment where the cleaning rods were stored on these rifles was behind the buttplate. There is a brass trap door in the buttplate that slides up and down to allow access to the cleaning rods. There is a L shaped spring on the underside of the buttplate that puts tension on the trap door to keep it from falling open. This screw goes through the top ;tang ; of the buttplate and threads into that spring. NOTE: on the 1876 the first 300 that came from the factory used a screw that went from the underside of the buttplate, through the spring and threaded into the top tang of the buttplate. On the 1866 the screw that attached to the spring to hold the curved trapdoor closed on the gunmetal buttplate was inserted from the inside, passed through the spring and screwed into a threaded hole on the underside of the top tang of the buttplate and you could NOT see it from the outside (this is not the screw for that style). On the 1873 prior to 29,500 a different screw was used. If your serial number is after approx. 29,500 this is the correct screw.
