This is the Magpul MOE M-LOK Vertical Grip (MVG) for M-LOK handguards. 

Features:

• Lightweight polymer construction
• Attaches directly to M-LOK compatible handguards and fore-ends
• No additional Picatinny rails required
• Magpul TSB texture for improved grip and control
• Shorter, rounded length
• Optimized for use with the “thumb-break method”
• Includes all necessary hardware
• Includes basic grip cap and mounting hardware
• Made in USA

This is a must-have upgrade for modern rifles. Pick up one today!

Resources:

M-LOK Description and FAQs
M-LOK Installation Tips