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. Adjustable Vise Pins hold the block at the optimal working angle and the Lock Knob ensures the upper receiver stays exactly where you want it. Get smart about the way you work on your firearm with the Lug-Lok Upper Vise Block PRODUCT OVERVIEW Fits .223/5.56 AR15s Vise Pin Retaining Holes Lock Knob Retaining Holes 7075-T6 Aircraft Grade Aluminum Star Chamber Locking Lugs Upper Receiver Lock Knob Alignment Flange 2 Stainless Steel Vise Pins