here is my problem i have an ls head and i tried to put regular 14 mm spark plugs 3 of them fit but the other one is way bigger i am guessing it was re threaded or something maybe to a 18 mm with that tool but now i dont know what spark plug to use since i lost the spark plug that was originally there i am sure someone has had this problem before please help me i need my car running asap thank you

 

i kno a kid with this problem, he also had a stripped thread which we ended up making it larger to a 16mm, i guess it depends on what u retapped it at, my mechanic ended up helpin us out on which spark plug to get for it that wud match the stock ones, im gunna ask him what it was, but if urs is 18mm it could be very different

 

ok thanks bro