The Fab Defense M4 Picatinny Under Rail for AR-15/M4/M16 Handguards Black adds a clean, continuous mounting surface to standard two-piece carbine handguards. Built around the UPR 16/4 Universal Picatinny Rail design, it compensates for the natural angle of the handguard so attached accessories sit properly aligned with the barrel.

This rail is ideal for mounting vertical grips, lights, lasers, or other Picatinny-compatible accessories on rifles that use traditional M16, M4, or AR-15 handguards. Its reinforced polymer construction keeps weight low while maintaining durability for training, range work, or general-purpose rifle setups. The design reflects Fab Defense’s focus on practical ergonomics and dependable accessory mounting solutions.

Key Features:

• Manufacturer: FAB Defense
• Model: UPR 16/4 Universal Picatinny Rail (FX-UPRB)
• Type: Picatinny Rail
• Material: Reinforced Polymer Composite
• Finish Color: Black
• Compatibility: M16/M4/AR-15 Handguards
• Standard: MIL-STD 1913