Exhaust Manifold Gasket, 1949-1987 Six Cylinder. Multi-Layer Gasket Manufactured by XKs Unlimited. Sold per each. Two required per engine. This composite gasket has two graphite layers bonded to a steel core and is ideal for vintage applications such as Jaguars. Here is a more complete explanation: Scuffing occurs due to the big difference in expansion characteristics of the aluminum head and the cast iron manifold. Both "grow" when heated, but the aluminum grows faster and more than the iron. As a result, both surfaces slide against the gasket face at a different rate, resulting in material being scrubbed off the gasket face over time. Kind of like a pencil eraser over paper. As small bits become dislodged on the gasket face, leaks can occur, and eventually the gasket burns through. The graphite material allows the two surfaces to "slide" across the face of the gasket (due to graphite's lubricating qualities) and not destroy the gasket. This material was developed in the early 1980s when Honda had a huge head gasket failure problem with conventional gaskets. Same reason -- aluminum head on a cast iron block. Graphite solved the problem and was adopted by Honda as OE and came into wide use in the aftermarket for all kinds of gaskets, particularly head and manifold gaskets, where dissimilar metals are used. It is more costly than conventional material and is not used as much now by OE, due to the development of laminated steel gaskets and chemical sealing materials. But the OEs have a big advantage in that they are always joining two "known flat" surfaces. In the aftermarket, we have to be concerned with sealing parts that are not always perfectly flat or perfectly surfaced, so these thicker composite gaskets work best. They allow for some imperfection in the joining faces, imperfect torque, etc.