Midwest Industries Gen 4 M-Series Handguard, M-LOK, Fits AR-15 Rifles, 13.375, Black MI-G4M13.375 The Midwest Industries Gen 4 M-Series Handguard features a continuous Mil-Spec M1913 Picatinny top rail" M-LOK accessory mounting slots on 7 flats along its length and four anti-rotation QD sling swivel mounting points. It is constructed of 6061 aluminum with a type 3 hard coat anodized finish. Includes barrel nut" barrel nut wrench" torque plate and one 5-slot polymer rail section. Gen 4 M-Series Handguards are super slim at 1.5" outside diameter and 1.3" inside diameter. Midwest Industries is a proven leader in the firearm industry. Made in the USA" focusing on the small details to make your rifle platform better.