Breakthrough Clean Technologies, Upper Vice Black, For AR15, Designed to Be Inserted in to Barrel Lugs NEW WARNING Warning WARNING California Prop 65 WARNING. These products contain a chemical known to the state of California to cause cancer, birth defects and other reproductive harm. Lead: Cas-No. 7439-92-1 Designed to Be Inserted in to Barrel Lugs Securely Holds Firearm in Vise Removable Plug Locks Device without Damaging Receiver Product Description Breakthrough's AR15 Upper Vise Block is made from durable material which provides a solid surface to secure your AR15 in a vise.