I'm telling you...this is what you want:
The Percy's Seal-4-Good Reusable Flange Gaskets are multi-layered and made from a special "Dead Soft" Aluminum, which conforms to header flanges for the ultimate seal. Since the Seal-4-Good is made from multiple layers of dead soft metal, it easily conforms to small imperfections that a copper gasket simply can not. Due to this construction, these gaskets will not blow out or burn out when properly installed.
Percy's Seal-4-Good collector gaskets are referred to, by many, as the "best on the market". These "Dead Soft" aluminum gaskets seal far better than competitive copper gaskets. Available in 2 1/2", 3", and 3 1/2" sizes.