Two heavy-duty, black oxide-coated high-carbon steel 6mm inserts are stronger than the original cast iron manifold material; removable. For the Nino ProKit. Get these heavy-duty inserts for a permanent repair that is stronger than the original fastener itself. Heavy-duty black oxide high-carbon steel inserts renew or repair the threads, eliminating the need to remove the exhaust manifold. Another key benefit is that they are removable, and because they are made from hardened carbon steel and coated with black oxide for corrosion resistance. Because of this, these inserts are stronger than the cast iron manifold material they restore. With thick walls for durability these high-quality precision-made inserts will withstand the high manifold temperatures of the Ford 6.7L Power Stroke diesel engine.