The FUSION Folding Backup Iron Sight attaches directly to the MODTAC U-RAC, RAS-XL, or Unity Tactical FUSION Micro Hub.  The Folding Backup Iron Sight is compatible with all standard AR15 rear BUIS, and is fully adjustable for elevation.

Description from Unity:

FUSION™ is a modular, multi-purpose mount designed to give the end user extreme flexibility in mounting options. It was engineered from the ground up to provide a strong mounting base with the widest range of configurations while remaining lightweight and low profile.

Material: 6061-T6 Aluminum
Finish: Type 3 Hardcoat Anodized