The FAB Defense FXRBS Rear Back-Up Sight for AR-15/M16/M4 delivers a dual aperture, low folded profile folding rear sight with spring-locked deployment that locks securely into position when not in use and deploys smoothly when needed. Built for reliability on the AR platform, this folding rear sight combines durable polymer with metal components, delivering a lightweight yet rugged sighting solution that stands up to field use and rigorous range sessions. Its windage adjustment allows precise zeroing to match your preferred optics or iron-sight setup, while the low profile design minimizes snag hazards and preserves aiming clearance during rapid transitions between sights. The FXRBS is engineered to fit AR-15 variants, providing a versatile option for hunters, competition shooters, and duty or backup configurations where a compact, quick-access iron sight is advantageous. With its dual aperture system, you can quickly switch between shooting scenarios, from close encounters to longer-range targets, ensuring reliable alignment without sacrificing speed. This sight blends practical engineering with a clean black polymer and metal build, making it a smart upgrade for any AR-15 platform that demands dependable, battle-ready back-up capability.