The Midwest Industries Same Plane Low Profile (SPLP) Back Up Rear Sight features an extremely low profile dual aperture design, and sits at only .4375″ when folded. – Locking detent with large surface area for maximum strength. – Same ball detent battle proven design of #MCTAR-ERS- Lock detent button with stepped down turns, to provide a surface you can grab onto if your hands are muddy or wet. – Micro style windage knob featuring the same MOA Adjustments as the standard M-16: .65 MOA on M-4 type rifles / .49 MOA on A-4 type rifles. – Made in USA