This ERS (emergency rear sight) flip up rear sight has an A2 style dual aperture and thick rugged pivot ears. Super smooth ball bearing pivot detent automatically locks in the raised position. Same style windage knob as on the standard M16 (.65 MOA on M4 type rifles, .49 MOA on A4 type rifles). Constructed of 6061 aluminum and hard coat anodized for a lifetime of service. MADE IN THE U.S.A.