The Wheeler Engineering® Delta Series AR Upper Pic Rail Vise Block is designed to securely hold basically any AR upper receiver. It 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 pic 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.