Phase 5 Weapon Systems Lo-Pro Slope Nose Free Float M-LOK Rail, 15, Black Finish, Steel barrel nut and mounting hardware included, Built-in QD Mounts with Internal Stops LPSN15MLOK The 15" LO-PRO SLOPE NOSE M-LOK Free Float Quad Rail was developed to accommodate the features of their 7.5" LPSN quad rail to a longer 15" version. The LPSN15 M-LOK was inspired by beneficial features that shooters have requested and demanded from them and other manufacturers. M-LOK is a modular locking accessory mounting system that is a direct attachment method for hard mounting accessories to a negative space mounting point. The details and level of care during the manufacturing of the LPSN15 M-LOK makes it the perfect choice for your AR-15 rifle build.