The Vism AR-15 back up flip up rear sight is a low profile spring loaded A2 dual aperture large and small sight that is fully adjustable for windage. AR-15 BUIS rear sight mounts to Picatinny Mil-STD 1913 rails. Knurled windage knob makes adjusting the windage an easy task. The AR-15 back-up iron sight flips-up and deploys with a push of a button. Aircraft grade aluminum main body with steel A2 dual rear aperture, windage knob, and adjustment screw. Dimensions: 2.4"L X 1.2"W X 0.8"H. Limited Lifetime Warranty.