AR-15 Upper Vise Block Works Two Ways...Secure By Picatinny Rail OR By Pinning Thru Take-Down LugsThis innovative AR vise block will secure AR-15 uppers by engaging the takedown lugs on the bottom of the receiver. By reversing the direction it will secure most AR-10 style uppers in the same manner. In addition it will secure any Picatinny Rail on a hi-rise, standard flat top or many other integrated rail guns by sliding onto and clamping the rail. The durable machined aluminum construction and precise tolerances ensure a secure hold essential for removal and installation of stubborn barrel nuts as well as a variety of other tasks.