This Lyman manufactured No. 42 receiver peep sight is for the model 5 bolt action rimfire rifle and is unmarked except for the manufacturers name on the base portion. This sight is missing its fold down (forward) peep and is threaded for an eye cup (present). The overall condition is very good exhibiting a brown patina mixed with original blue finish. The two mounting screws are included. Your rifle may require drilling and tapping to install.  (file photos)