Manufactured from premium fuel-resistant materials that will not creep, crack or become brittle. 4.125" big bore is a popular big bore for performance-oriented Harleys, as it builds serious cylinder pressure and can use the extra sealing properties of the MLX head gaskets. Center layer is folded over on top of itself which simulates an O-ringed head and adds a targeted torque load right at the combustion seal where you need it. MLX head gaskets are essential for all Twin Cam applications using a Turbo, high compression, nitrous or any power adder modifications. Proprietary high-temperature coatings along with embossments provide a micro seal for fluids against the head and block surface. Require no special machining and are installed like a regular MLS head gasket. Sold in pairs for popular bores and thicknesses. Made in the USA.