This innovative AR 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.Specifications and Features: For use with a securely mounted, 6" or larger bench vise (sold separately) The block's Picatinny rail dovetail clamp is a precision surface. Care must be taken during use and storage of the block to avoid damage to this surface. Clamping items into the block's Picatinny rail clamp may result in minor surface or finish marks. The Picatinny rail clamp is not limited to upper receivers alone. It is compatible with any other part that has a Picatinny rail interface.