Geissele Automatics 051656B: The Super Modular Rail (SMR) MK4 M-LOK is Geisseles ultra-rugged M-LOK option. These rails are purpose-built and feature integrated M1913 picatinny rail sections at the fore of the rail in the 3, 6 and 9 oclock positions. Maximum venting for heat dissipation also dramatically reduces the rail\'s overall weight, while maintaining its same strong and rigid platform. Utilizing Magpul\'s M-LOK technology at the 3, 6, and 9 o\'clock positions, as well as the upper 45 quadrants.