Constructed from spring steel or graphite. Spring steel gaskets are made from a stainless steel shim design coated with a.0001" thickness of silicone on both sides. Graphite material is impervious to fuels, coolants and oils. Engine case rebuild gasket kits include all gaskets needed for a lower end rebuild (base gasket not included). EST?(Extreme Sealing Technology) Top End Kits; critical seal and superior durability from technologically advanced materials; meets and exceeds O.E.M. specifications; kit contains valve stem seals and exhaust gaskets. Top End Kits contains head, base, exhaust, reed and power valve gaskets (where applicable) for complete top end rebuild.