This finger lever spring attaches inside on the left of the receiver.(the side with out the Loading gate (spring cover)) This replacement spring functions to keep the finger lever (cocking mechanism) secure to the lower tang after cocking the Winchester model 1873. This is not the Uberti replacement spring! These are high quality and made specifically, and are exact replacements Winchester 1873 rifle. The screw that you need for this spring is part number wp604-a.