This is a GG&G, Inc. known as the Vertical Forend Grip, model GGG-1169.
GG&G's AR-15 Vertical Forend Grip offers a very stable vertical grip and the new waterproof compartment will now accommodate an AR-15/M16 spare bolt. The interior of the "O" ring sealed waterproof compartment has been re-configured to securely hold the bolt in place. Without the spare bolt stored" the waterproof compartment is large enough to securely hold two AA batteries and or two CR123 batteries. Three N type batteries" firing pins" ejectors" extractors or other small replacement parts for your weapon system can be stored in the compartment but the user needs to pack additional material" so as to eliminate rattling. Unlike other forward hand grips in the marketplace which are molded or injected plastic" all parts of the GG&G Vertical Foregrip are CNC machined from solid black Acetal cold polymer for durability and low heat absorption.
No special tools are needed for installation or adjustment
Waterproof compartment has a Tri-grip cap designed to be non snag
4.5 in length