The Delta Series AR-15 Upper Vise Block is optimized for left hand and right hand Mil Spec A2 upper receivers with carry handles, as well as flattop style receivers. The Block allows you to safely clamp on to your AR-15 upper receiver in a vise holding it securely without twisting, crushing or marring the finish. It is the ideal product for torquing a barrel on, removing a stubborn barrel nut or for simple gun maintenance and cleaning. It is made of a high pressure, solvent resistant polymer material which can withstand almost anything you can throw at it. The Delta Series AR-15 Upper Vise Block truly is the all-around product for your AR-15 gunsmithing, maintenance or cleaning needs. As an added bonus it includes a receiver insert with a gas tube alignment system, making sure your gas tube is always in line when installing a barrel and torquing a barrel nut. Durable design holds receiver securely Fits left and right-hand Mil Spec A2 upper, as well as flat top receivers Receiver insert with gas tube aligner included.