The 2 piece Slimline Drop In Rail available in 7" or 9" is a non free-floating replacement railed hand guard for all M4/AR15 carbine length plastic hand guards. The design ensures a solid mounting platform. Rail systems are machined from T6061 hardened aerospace grade aluminum extrusions. U.S. M1913 compliant rails. Milled/ engraved slot positions and aiming modular /threaded mounting holes. Finished in MIL-A-8625 Type III Class II Hard Coat Anodizing. Non-rotating QD Sling Swivel Holes. Made in the USA. Made by US Govt Contractor to Mil-STD 1913 picitinny rail face specifications. No gunsmithing is required.