AR-15 Upper Receiver Vise Block Kit This Vise 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. This Block is the perfect product for torquing a barrel on, removing a stubborn barrel nut, screwing on a free-float forend, or for simple gun maintenance and cleaning. Optimized for left hand and right hand Mil Spec A2 upper receivers with carry handles, as well as flattop style receivers. Other AR-15 variants may be adapted with special attention to potentially non-conforming surfaces or features. It is made of a high pressure, solvent resistant polymer material... Very tough and durable. Bonus Feature - This AR-15 Vise Block Kit includes a receiver insert with a gas tube alignment system. This assures gas tube alignment when installing a barrel and torquing a barrel nut.