M4 handguard rail adapter for USGI AR15 plastic round handguard. Rail is Picatinny/MIL-STD 1913 tapered to match the handguard of the standard GI M4 handguards and A2 rifle length handguard. Black anodized aluminum construction. Rail includes two mounting screws and flanged nuts. Allen wrench tool also included. Length: 5.9" The taper in the rail will make accessories mounted to the rail parallel with your bore. More mounting holes for flexible mounting and increase ventilation. The ends of the rail have been rounded off for more comfort and to make it less snag prone.