Real Avid Lug-Lok Upper Vise Block - Support your build with the strongest part of your AR15. The Lug-Lok Upper Vise block utilizes the strength of barrel lugs to safely secure AR15 upper receivers while you work, rendering clamp-style blocks obsolete. The non-marring, aircraft-grade aluminum block slides through the upper receiver and into the star chamber of your barrel. This takes the pressure from torquing away from weak, damage prone parts and puts it squarely on the steel lugs. Fits .223/5.56 AR15'sVise Pin Retaining HolesLock Knob Retaining Holes7075 T6 Aircraft Grade AluminumStar Chamber Locking LugsUpper Receiver Lock Knob2 Stainless Steel Vise PinsAlignment Flange