Iridium is just a type of metal. Since it's harder than the copper (or whatever) that makes up the electrode of a standard spark plug, it can be refined into a finer point with no degradation in longevity. In theory this will give you a better spark. Some people swear by them. We have found them to hold up better in our racing applications over a standard plug in the real world, so they aren't all just hype.
Matt
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