The UTG Pro Model 4/AR15 Carbine Length Drop-in Quad Rail offers easy installation with no modification to the barrel. The top/bottom two-piece design has integral spinal cords/alignment housing for a perfect fit with the barrel nut and round front cap. It is precision CNC-machined from from aircraft aluminum with anodizing/engraving. The four Picatinny rails each have 14 slots with great zero-retention capability for all installed accessories. This quad rail system is designed to fit carbine-length Model 4/15 with a standard AR15 gas tube. It includes black rubber rail guards, and has a black anodized metal finish. Note-This quad rail system is designed to fit with standard AR15 gas tube. The compatibility with any special piston system is not guaranteed. Made in the USA.