This is a Daniel Defense Vertical Foregrip, model 21-067-05028-011.
Daniel Defense's Vertical Foregrip" Mil-Spec + Picatinny now includes soft touch rubber overmolding for enhanced grip" wet or dry. Inside the grip is a Dual O-Ring" water tight storage compartment capable of storing small parts. This vertical grip is extremely lightweight and utilizes a simple yet durable mounting method for 1913 picatinny rail systems. Not Compatible with KeyMod or M-Lok rail systems.
Features:
Picatinny Compatible Attachment System
Ergonomic Design
Mil-Spec + Finish (Brown/Daniel Defense)
Length 4.5" width 2" thickness 1.38"