This is a SB Tactical Stabilizing Brace known as the SBA3, model SBA3-03M-SB.
The SB Tactical SBA3 Stabilizing Brace for AR/M4 is designed for all platforms capable of accepting a mil-spec carbine receiver extension. The SBA3 is 5-position adjustable" dramatically enhances versatility" and features a minimalist design with an integral" ambidextrous QD sling socket.
Features:
For AR/M4
Minimalist design
5-position adjustable
Includes 7075 mil-spec carbine receiver extension brace and adjustable nylon strap