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At the price and potential hassle of a helicoil for $30 I'd just buy a new head for $45. And more importantly torque your spark plugs correctly. You can tighten them and then do the quarter turn past hand tight only one time on a new plug. After the crush washer is crushed then you have to torque them and it is a very light torque, lighter than most people assume. For 10mm threads you're asking 7-8 lbs-ft max.
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