This is a TROY Rail known as the Enhanced, model SRAI-DID-D7BT-00.
The Troy Enhanced Drop-In Rail is a non free-floating direct replacement for all M4/AR15 Carbine length plastic hand guards with a round end plate. The Troy patented clamping design ensures a solid mounting platform and provides a true optical mounting platform that increases the modularity and accuracy of the M4.
Features:
Drop-In Installation
Quad Rail
QD Swivel Sockets