This head gasket is made of three layers of steel and is viton coated. The viton coating means you don't need any sealant. It is designed for high performance engines and is 0.040" thick. Also good for aluminum heads because it doesn't have a compression ring. This is a modern very good head gasket. We've used this on a race motor that melted a piston and had no head gasket issues. This was the only version available, but now they have a smaller bore hole version for 1275's bores 40 or less. RHG-101