doorman --HeliCoil is the name of a company that was the originator of the "wound-wire" type of thread repair insert, but wound-wire inserts aren't the only type of thread repair insert that the HeliCoil company makes. Wound-wire inserts -- what most people mean when they use the HeliCoil brand name as a generic descriptor -- ARE used to repair spark plug threads, but they make a third-rate repair. Solid inserts are much better suited to this particular job. The queen of the solid insert is the Time-Sert, but the installation tooling is expensive enough to make the Time-Sert a take-it-to-the-machine-shop proposition for most of us. Next step down are a couple of inserts that are essentially glued in place. My personal favorite is the EZ-Lok insert (check their website at www.ezlok.com ), but the HeliCoil company's brand of solid insert, which they call Sav-A-Thread, is probably as good. John
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