This is the dust cover stop 1873 and 1876 Winchester lever action 2nd and 3rd model. (also called the mortise cover stop) This little part screws on the underside of the dust cover (part number wp606). The extractor hooks onto it and pulls the dust cover back opening the top of the receiver. These are ORIGINAL PARTS. The SCREW that holds this part onto the dust cover is part number wp161-a wop or wp617-a.