This Wheeler Engineering Delta Series AR-15 Upper Receiver Vise Block is a vital tool that enables the user to securely clamp an upper receiver into a bench vise without fear of crushing twisting or damaging it in order to perform critical assembly disassembly or maintenance tasks. It is ideal for use in torqueing barrel nuts to the proper spec attaching or detaching a muzzle device and is even useful for cleaning a rifle’s bore properly from the muzzle end with a cleaning rod. Manufactured from durable solvent resistant black polymer the clamp is compatible with A2 Uppers with an Integral Carry Handle as well as A3 Flattop Upper Receivers. Includes a Polymer Internal Receiver Insert to protect the receiver from crushing when the clamp is tightened and also a Gas Tube Alignment Pin for ensuring a barrel nut is properly aligned to allow clearance for the rifle’s gas system.