The Echo Keymod Rail is a free-float rial that has oversized cutouts along the top spine of the rail body to help mitigate the weight penalty, while keeping the rifle sturdy. The barrel nut locks up with the rail via six hex bolts and timing shims used during the installation process. The Echo rail retains its slim profile from its base to the muzzle end. This 15.2" rail is constructed of 6061-T6 aluminum with a black hard coat anodized finish. Note: The Echo Keymod Rail does not include timing shims.