The Wheeler Engineering Delta Series Vise Block is an innovative and versatile tool that is designed for compatibility with almost any AR-15, AR-10 or LR-308 upper receiver. The Delta Series vise block is capable of accommodating such a wide variety of AR-type uppers because it can be attached in 2 different ways. The first method uses a pair of steel detent pins to engage the upper at its takedown and pivot pin lugs, with a set of properly sized and spaced pin holes provided for both AR-15 and AR-10 variants. The second option is to slide the vise block onto an upper receiver's Picatinny top rail and clamp it in place. Constructed of durable extruded aluminum, the Delta Series vise block is the perfect device to hold an AR upper safely and securely within the jaws of a bench vise in order to perform regular maintenance or critical assembly/disassembly procedures such as torqueing off a stubborn barrel nut. Technical Information 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 daMagazinee 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.