In the last 12 years I've used other brand plugs that were suited for my Volvos. Never again, aftermarket plugs start to gap after 15k. Last set of NG& plugs gap open to .50 thous. Replaced all after market plugs with OEM Volvo plugs. I don't know what it is but, all the aftermarket plugs open gap from .34 to .52 thous. I use oem Volvo plugs now, they're three times the price, but they won't open gap and stay set..