These gas blocks along with Aero’s gas tubes create an efficient and reliable gas system for your AR15 or AR 308 rifle build. Features: Fits barrels with .875 Outer Diameter Constructed from 4140 hardened steel Choose No Aero Logo or Aero “A” Logo blocks Nitride or Phosphate coating Low profile for easy fitment Set Screws are Steel 10-32 x 3/16 Knurled Cup Point Made in the USA *Roll pin not included*