The Daniel Defense DDM4 Rail, found on many DDM4 firearm configurations, features an optimized one-piece, free-floating architecture. This design results in the ergonomics and proven durability users demand while maintaining the lightweight characteristics they expect from 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 15.0 is compatible with low profile gas blocks on barrels 16" and longer with gas systems at Rifle 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 temperature resistant Santoprene. Features: a Lightweight Free Floating Barrel Design a Steel Barrel Nut a Uninterrupted Upper Rail Platform a Integral Sling Swivel Attachment Points with Limited Travel a Patented Bolt-Up System a Mil-Spec 1913 Picatinny Rails a Installation requirements: Bolt-Up System Barrel Nut Wrench (Supplied), Allen Wrench (Supplied)