This Winchester manufactured slide arm bridge retaining screw is for the model 120 slide action shotgun with serial number below L2,000,000 and is in near excellent condition with light wear. However, I found an unaltered model 120 shotgun with serial #L2114967 which had a second variation breech bolt slide with the threaded screw like the first variation and notched on the underside like the third variation breech bolt slides, a late variation slide arm bridge and this screw in place.  (file photo)