This is a F.A.B. Foregrip, model FX-FGGSB.
The FGG-S Tactical Folding Foregrip enables an additional 'horizontal to vertical' grip option on your weapon" enhancing tactical versatility and performance. It is specifically designed not to interfere with handgun firing when in horizontal position and quickly transforms from a horizontal grip to a vertical grip.
Features:
Black finish
Easy and fast adapt/removal mechanism
Fits 1913 Mil-std picatinny rails