Troy Drop In Rifle Length Rails are direct replacements for all M16 and M4 carbine plastic hand guards. The Troy Patented clamping design ensures a solid mounting platform. The Rifle Length Rails provide a true optical mounting platform that increases the modularity and accuracy of the M4. No gunsmithing is required as the Drop In Rail installs in less than two minutes and provides true U.S. Military Specification M1913 rails at 12-3-6 and 9 o'clock. Troy Drop In rail systems are machined from hardened aircraft aluminum and anodized in MIL-STD Type III hard coat. - Black - 12"