Head GasketManufactured from premium fuel-resistant materials that will not creep, crack or become brittle4.125" 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 gasketsCenter 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