Basic flip-up sights for Picatinny rail, meant for Nerf. Down- open sights. Up- aperture. Uses a piece of filament as a hinge pin and 4-40 screws for mounting to the rail. The sight pieces should be a very very tight press fit. Press them in so that the nubs lock into one of the holes aligning the hinge pin hole appropriately. Push filament in to act as hinge pin. Trim filament, recommend you glue the filament in place on the base piece, and you're good to go.