Unfortunately, spark plug threads are similar to oil threads. The plugs you purchase will work in your car. It's up to you to note if their performance is perfect or you notice anything off.
I stick with OEM but that doesn't mean I would piss on the iridium plugs.
I've owned an '84 Alfa Spider since 1993. Alfa calls for an OEM plug (loge) is basically no longer available. Alfa also calls out a Champion plug as an alternative. Ive never had luck with the champion plug, yet other Alfa owner swear by them. I've run $1 Autolite copper plugs and had no problems. The 'go to' plug for Alfa's right now is an NGK plug (non iridium). I tried the NGK iridium plug in the Alfa and the car did not run or idle as well as with the other plug.
Point is, my experience is with my car. It isn't wrong but means nothing other than a data point to Spider owners.
Try your plugs...If you like them, great, if not, try something else.
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