Premium Grade Parkerized AR-15 Rifle Barrel, 16\" Contour M4 Barrel,1 in 8 twist Gas port drilled for carbine length gas set up, and threaded for comp.Barrel Extension in rear with M4 feed ramps... drilled with a .070\" gas port diameter at carbine length. It has a .750 gas block diameter ready to install into receiver.This barrel is marked as being chambered 5.56 NATO - Set up for carbine length handguards. Don\'t forget the AeroShell 33MS Mil Spec Armorer\'s Grease!