These upper receiver / handguard assemblies give you the ability to quickly change a rifle barrel to different length or caliber options. The 12-inch Free float handguard features 6 panel mounting locations, QD Sling swivel pockets, and includes 6 snakeskin panels with screws. Additional panel sets ( 3 ea of sam type panel in each kit) are availble in KeyMod, M-Lok, and “Frag”. Also, 5 slot or 11 slot Picatinny Rail pattern panels are available ( these are sold individually), (MCS Interchangeable Panels) The six-inch version features a quad rail handguard. The upper is crafted from 7075 T6 aluminum, while the handguards are made from 6061 T6 aluminum. They are compatible with the Windham Weaponry Multi-Caliber System and the MGI Hydra system.