M40A1 Unertl / USO MST-100 Parallax And Sighting Tool. This listing is for a parallax adjustment tool only, no scope is included. This tool works the same as the original but has 1 MOA division lines and 1/2 MOA hash marks in between the lines. The underside has 3 feet, that fit over your elevation and windage knobs hold it in place while you make sight adjustments.