The PMA free float keymod rails are exactly what you need to complete your project rifle. This style of KeyMod Handguard is a lightweight free floating handguard featuring a continuous Mil-Spec 1913 Picatinny rail. The rails themselves come in 7", 9", 11" and 15" to meet all of your requirements. Constructed out of 6061 T6 Aluminum and hard coat anodized for superior finish and strength. The light weight design can support lights, sights, lasers, and all other accessories you need. Unlike other after market rail systems these line up perfectly with your upper receiver. The quality and price come together for the best combination of value and style. The inside diameter is 1.3" to fit most gas blocks and muzzle devices.Fits Modern Sporting Style RiflesMaterial 6061 T-6 AluminumLength 15 InchesInterior Diameter 1.41"Outer Diameter 1.58"Weight 8.3ozFinish Anodized BlackFree Float YESIncludes Free Float Rail, Steel Barrel Nut, 3 Steel ScrewsWarranty Limited Lifetime100% Made in the USA.