This is a Ergo Grip Rubber known as the Sure Grip, model 4009-OD.
The Original Ergo Suregrip AR Grip Kit A/T (aggressive texture) is ergonomically designed to fit all AR-15/M16 rifles. SUREGRIP models feature an overmolded rubber-like surface for a more positive grip and are designed to help prevent fatigue and enhance weapon control. Each ERGO Grip comes with their patented GAPPER and uses existing grip hardware for installation.
Features:
Fits AR-15 type firearms in .223 and .308
Ergonomically correct finger grooves
Virtually impervious to oils and solvents
Comes with The Gapper
