The Geissele SMR (Super Modular Rail) HK416 MK15 MLOK brings the reliability and durability you would expect from a Geissele product. The rail system utilizes the stock HK barrel nut while incorporating strength, rigidity and modularity. Made from 6061-T6 aluminum and finished in type 3 hardcoat anodize, the SMR HK416 MK15 meets military specifications. The HK M-LOK Rails have M-LOK mounting options at 3, 6, and 9 o'clock positions, as well as featuring a full picatinny rail along the top and shortened picatinny rails on the forend. Height: 2.61"" Color: Black or DDC Lengths: 10.5"" and 14.5" Inner diameter:& Mfg: Geissele Automatics