FAB Defense FXRBS Folding Rear Back-Up Sight for AR-15/M4/M16 - Black
$55.20
- Type:
- Sights - Rear
- Firearm Group:
- AR Platform
- Firearm Fit:
- AR-15
- Windage Adjustment:
- Yes
- Frame Material:
- Polymer/Metal
The FAB Defense FXRBS folding rear back-up sight for AR-15, M4, and M16 platforms gives you a reliable secondary sighting option that stays low and out of the way until you need it. Whether you're running a primary optic that needs a failsafe, setting up irons as your main sight system, or building a transitional carbine, this rear sight delivers fast target acquisition without the bulk. The distinctive angle-wing shroud design works with any compatible front sight to create a precise optical tunnel that helps you stay centered and speeds up your aim-in, especially in variable lighting or when you need to move fast.
Deploy instantly with the spring-locked mechanism—no creep, no hesitation, no tools required. The folded position lies low and smooth against your upper receiver, so it won't snag on sling gear, plate carriers, or brush when you're moving through cover. Windage adjustments are tool-free and lock positively in place, so you can dial it in at the range or in the field without fumbling for hex keys.
The FXRBS is built tough: high-grade polymer and metal construction that handles hard use. The dual apertures—3mm for extended eye relief and rapid acquisition in low light, and 1.5mm for precision and shorter sight radius—let you pick the setup that matches your shooting conditions and front sight height. Pair it with FAB Defense's matching front sight for a fully integrated backup sight system, or run it standalone with whatever front option you prefer.
Key Features
- Instant spring-locked deployment with no-slip mechanism
- Dual-aperture design: 3mm (extended eye relief, low-light use) and 1.5mm (precision, shorter radius)
- Angel-wing shroud centers your sight picture and speeds target acquisition
- Low folded profile stays flush and snag-free
- Tool-free windage adjustment with positive detent locking
- Durable polymer and metal construction
- Fits AR-15, M4, M16 platforms
Specifications
| Brand | F.A.B. Defense |
| Product | FXRBS Folding Rear Back-Up Sight |
| Compatibility | AR-15, M4, M16 |
| Apertures | 3mm and 1.5mm, user-selectable |
| Mechanism | Spring-locked instant deployment |
| Material | High-grade polymer and metal |
| Position When Folded | Low profile, snag-resistant |
| Windage Adjustment | Tool-free with positive detent lock |
| Color | Black |
Frequently Asked Questions
Will the FXRBS work as a standalone rear sight, or does it require the matching FAB Defense front sight?
The FXRBS functions as a complete rear sight on its own and works with any compatible AR front sight. FAB Defense makes a matching front sight that pairs with this rear to create an integrated optical tunnel system for enhanced alignment, but it's not required—use this rear sight with any front sight option you prefer.
What's the difference between the 3mm and 1.5mm apertures?
The 3mm aperture offers extended eye relief and faster target acquisition, especially in low-light conditions where a larger sight picture helps. The 1.5mm aperture gives you a tighter sight picture for greater precision and works best with a shorter sight radius. Both are instantly selectable, so you can switch between them to match your shooting conditions and setup.
Does the FXRBS fold flat enough to coexist with a magnified optic?
Yes—the low folded profile is designed to be smooth and inconspicuous and won't interfere with most mounted optics on the receiver. When folded, it remains flush and snag-free.
Will I need tools to adjust windage or deploy this sight?
No. The FXRBS deploys instantly via the spring-locked mechanism, and windage adjustments are completely tool-free. The positive detent lock keeps your zero in place without requiring external tools.
