Aimsports AR-15/M4 flip up rear sight feature dual aperture for long and short range, ball bearing pivot detent, automatically locks into position when raised, flip-up posi-lock design to guarantee zero and A2 style dual aperture, Small Aperture: 0.070″, Large Aperture: 0.200″. 0.65 MOA on M-4 type rifles and 0.49 MOA on A-4 type rifles.