This Delta Carbine Rail is a 12 modular quad rail with two built-in QD swivel mounts. The two-piece drop-in system requires no gunsmithing to install, requires no modification to the firearm. Troy's drop-in free-float rails are built off a rock-solid rotary clamping system; do not require removal of the delta ring, barrel nut or fixed front sight. It installs in minutes and offers an extended forearm while allowing the user to keep the existing fixed front sight post. The Delta modular rail system allows the addition of smaller rail segments (not included) where needed without the added weight of a full-length quad system. Designed for firearms with A-frame sights. *Not compatible with .308 ARs and Ruger AR 556 due to the built in QD at the bottom of the A2 front sight. Made in the USA.