SPARK PLUG, AND MAIN METAL FITTING FOR SPARK PLUG

摘要

A spark plug superior in salt corrosion resistance and stress corrosion cracking resistance is provided. The park plug includes a metallic shell coated with a composite layer which includes a nickel plating layer and a chromate layer formed on the nickel plating layer. The spark plug is characterized in that the nickel plating layer has a thickness A which satisfies a relational expression 3 µm ‰¤ A ‰¤ 15 µm and that the chromate layer has a thickness B which satisfies a relational expression 2 nm ‰¤ B ‰¤ 45 nm.