Daniel Defense. The DDM4 Rail's ergonomic design allows operators to maintain better control of the firearm. Limited rotation QD swivel attachment points are located at the front and rear of both sides of this rail system for tangle-free attachment for slings. A continuous picatinny rail on top provides the rail real estate for sights and accessories. DDM4 Rail 10.0 is compatible with low profile gas blocks on barrels 11" and longer with gas systems at Mid-length and shorter. Rail System includes all required hardware (Barrel Nut, Bolt-Up Plate, & Screws), tools (Barrel Nut Wrench & Allen Wrench), and 3 Daniel Defense Rail Ladders made of high temperatu Mfg: Daniel Defense SPECS: Fits - AR-15/M16 rifles. Construction - 6061-T6 Aluminum and Steel barrel nut.