The Super Modular Rail (SMR) MK8 M-LOK is Geissele's ultra-modular model. It is 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. The rail utilizes Magpul's M-LOK technology at the 3, 6, and 9 o'clock positions, as well as the upper 45 degree quadrants. The SMR MK8 is both versatile and modular, allowing the user to tailor their platform to his or her unique needs. NOTE: This rail is designed to work with Mil-Spec M4 upper receivers. The compatibility with billet receiver sets is unknown.