This is the Magpul aluminum Picatinny rail section for M-LOK forends and hand guards.

Once installed, you can attach various Picatinny rail-mounted accessories, such as lights and grips.

Features:

• Made from milspec-anodized aluminum
• Features beveled ends to reduce snagging 
• All hardware included
• Made in the USA

Resources:

M-LOK Description and FAQs
M-LOK Installation Tips