Primary Arms GLx MD-21S, Microdot, 21MM Objective, 2 MOA Reticle, Fits Aimpoint Micro Footprint, Anodized Finish, Black PA-GLX-MD-21S The GLx MD-21s is a high-performance micro dot optic, built for superior agility and precision from close-quarters to intermediate range. This red dot features an advanced solar failsafe system, supplementing your power supply to ensure the optic operates with maximum runtime.