Geissele Automatics 05827B: The Super Modular Rail HK416 MK15 M-LOK was designed to replace the standard rail on an HK416 or MR556 weapon platform. The rail system utilizes the stock HK barrel nut, but incorporates the strength, rigidity and modularity expected of a Geissele product. Made from 6061-T6 Aluminum and finished in type 3 hardcoat anodize, the SMR HK416 MK15 meets military specifications.