FAB Defense FXRBS Rear Flip-Up Sight — Black (AR-15/M4)

Description

The FAB Defense FXRBS is a low-profile, folding rear back-up sight designed for use on AR-15/M4/M16 platforms. It mounts to a 1913 Picatinny rail and can function as either a primary or auxiliary rear sight. The sight offers two selectable apertures — a 3mm aperture for longer eye relief and low-light speed, and a 1.5mm aperture for closer eye relief and precision. Constructed of high-grade polymer and metal, the FXRBS features an instant spring-locked deployment that resists slipping or deformation.

Key Specifications

• The sight mounts to a 1913 Picatinny rail for broad compatibility.
• Compatible with AR-15 / M4 / M16 platforms.
• Includes dual apertures of 3mm and 1.5mm for varied engagement distances and light conditions.
• Features an instant spring-locked deployment mechanism that resists slip or deformation.
• The low folded profile is smooth and snag-resistant for use on gear or in brush.
• Ergonomic angel-wing-shaped shroud helps center the image with most front sights.
• No tools are required for rapid windage adjustments with positive detent locking.
• Constructed of polymer and metal for a balance of durability and weight savings.
• Weight listed as 0.115 (unit not specified in source data).
• Finish / color is Black.

Engineered for straightforward, reliable operation, the FXRBS provides a practical backup or primary sight solution where a compact, fast-deploying rear sight is required. Its selectable apertures, positive windage detents and low folded profile make it a sensible choice for shooters seeking a durable, no-nonsense folding rear sight that integrates easily with standard AR-15/M4 rails.