This is a Yankee Hill Machine Co Grip known as the M-LOK, model YHM-5425A.
This ambidextrous vertical grip is a simple" lightweight" and cost-effective device which secures tightly to any M-Lok mounting system. The low profile vertical grip design provides a positive hand hold in a small package. Adequately sized to allow the hand to take control of the front of the rifle" but not large enough to get in the way.
Features:
Black finish
M-Lok grip without storage compartment
2.95 in height;Includes Allen wrench
