This is a Midwest Industries Sight known as the Flip Rear Sight, model MCTAR-ERS.
Midwest Industries ERS (Emergency Rear Sight) Flip-Up Rear Sight. All of Midwest Industries products focus on providing top notch quality and reliability you expect from products made in the U.S.A. Backed by Midwest Industries Lifetime Warranty.
Features:
A2 style dual aperture
Thick rugged pivot ears
Locking detent with double the locking surface for maximum strength;Lock detent button with stepped down turns;.65 MOA on M-4 type rifles / .49 MOA on A-4 type rifles
