Yankee HIll 7.28 Inch SLR-Smooth Series Forearm - Carbine Length. The SLR (Slim, Light, Railed) series have a profile that allows for most piston systems to be used while maintaining a top rail that co-witnesses with the upper receiver. Yankee HIll redesigned the top rail installes to create one continuous picatinny rail between the upper receiver and the handguard. NO EXTRA TOOLS are needed to install the SLR handguards! The smooth customizable version allows you to mount accessory rails to the sides.