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. The Picatinny rail on the bottom of the rail or the 6 oclock position is elongated in this version to more comfortably accommodate accessories. Maximum venting for heat dissipation also dramatically reduces the rails overall weight while maintaining its same strong and rigid platform. The MK4 M-LOK rail features M-LOK slots at the 3 6 and 9 oclock positions as well as the upper 45 quadrants. This allows the user to keep the weight on the rail system down while keeping the modularity and versatility to attach accessories as necessary.