Diopter front sight insert set

Old cased set consisting of barrel clamp that holds front sight insert. Four sight inserts. Three are round circles that have a small degree of magnification only in the centre of the circle and one post with no magnification. Inserts fit tightly into the holder and do not screw in. Holder clamp area is .75 inch (19mm) and has name on the side of it: “Shootwell” Production equipment Co. Inc., 5 Union Square, New York.