This is a Ergo Grip Rubber known as the ERGO 2, model 4010-DE.
The ERGO 2 AR Pistol Grip with Suregrip" is uniquely designed to allow installation on both .556 and .308 AR/M4 lower receivers without a need for spacer inserts. A traditional A2 sized inner cavity is compatible with many accessories available on the market. The ergonomically correct finger grooves provide a sure purchase under even the most extreme conditions.
Features:
Design allows installation on both .223 and .308 AR-15/AR-10 type receivers
Ergonomically correct finger grooves
Comes with The Gapper
