Not all solid copper gaskets are created equal. SCE uses premium 99% pure copper sheets rolled to our specifications (choice of 12 different thicknesses) and tested for uniform flatness to assure precise cylinder head-to-block alignment and eliminate uneven loading. After processing, each gasket is annealed to ensure optimum mating and provide measurable gains in-cylinder sealing, as evidenced by lower leak-down percentages. O-ringing recommended.