Geissele Automatics MK8, Super Modular Rail, 9.3 inch, MLOK, Desert Dirt Color. These rails are designed to give the user full modularity while maintaining a strong and rigid platform. Maximum venting at the lower 45-degree quadrants create maximum heat dissipation and also dramatically reduces the rail’s overall weight. (Shade Variations and Other Imperfections Are Normal Due to the Manufacturing Process. Designed to work with Mil-Spec M4 upper receivers. The compatibility with billet receiver sets is unknown).