Knight's Armament Picatinny Rail Rib Panels are lightweight polymer panels designed for Picatinny rails. They are ribbed for an enhanced grip and help insulate the support hand from barrel heat. Originally designed for use on the KAC M4 RIS and M4 RAS rails, these panels are compatible with many other railed handguards. Available rib configurations include: 2-Rib (1.65 in), 4-Rib (2.65 in), 5-Rib (3.47 in), 6-Rib (3.90 in), 9-Rib (5.48 in), and 11-Rib (6.15 in).