The Geissele Super Modular Rail (SMR) MK4 M-LOK is a high quality rail system that is used by the Federal Bureau of Investigation (FBI). It is designed to be strong, modular, and compatible with the M-LOK system. The SMR MK4 M-LOK features integrated M1913 Picatinny rail sections at the 3, 6, and 9 o'clock positions, as well as an elongated Picatinny rail on the bottom of the rail. This allows for maximum heat dissipation and weight reduction, while maintaining a strong and rigid platform. The SMR MK4 M-LOK also features M-LOK slots at the 3, 6, and 9 o'clock positions as well as the upper 45 degree quadrants. This allows for additional modularity and versatility, so users can attach accessories as necessary.