Original issue SIG PE90 Diopter sight. These diopter sights are installed easily by screwing the diopter set into the 300 meter marked setting. That setting has threading. The bead-shaped adjustable setting goes on the inside and the peep site screws on from the outside. These sights aided the SG90 in the accuracy field. The platform is already regarded for its precision but these sights help the user dial in more precision without the need for a scope. The diopter is marked: “Grunig & Elmigfrag SG90” Grunig + Elmigfrag is a company that produced very high precision rifles, and optics. There are based out of Switzerland. Their sights and rifles are designed to be competitive in the Olympic games.