This is a Diamondhead USA, Inc. Rail known as the VRS-T Free-Floating Handguard, model 2211.
Diamondhead's VRS T-556" 10.25" Free-Floating Handguard Rail" offers an uninterrupted rail extension and handguard in perfect alignment with the host weapon's flat top receiver. The VRS T rail replaces the factory delta ring and barrel nut. The VRS Free Floating Handguard System provides excellent flexibility of use by adding accessory rails and bumpers to the VRS for the required rail-mounted accessories.
Features:
Mounts on barrels with low profile gas block or can replace fixed front sight with a low profile gas block
Fits all M4/AR15/M16 variants