This is a B5 Systems End Plate known as the End Plate Sling Adapter, model AEP-1090.
Built from a single piece of steel" each QD End Plates creates a strong" flush fit for a lifetime of service. Its optimized design is great for users who want to minimize weight while adding an alternative Quick Disconnect attachment point. This anti-rotational connection works for both right-handers and left-handers.
Features:
Made of military-quality steel
Milspec phosphate finish
Resistant to corrosion