Just got another xj after not having one for a while. The only problem is it has a hard miss on cyl 6 i pulled the plug out today and some kind of spacer came out with it. It seems like it makes it sit out of the cylinder about a half inch more than the others.and only has about a 1/4" hole for the spark to come out of. Im wondering if this is somehow stock or what. I should also add without it the plug seems to not catch any threads.

 

Nevermind i engaged my brain i have never had a use for a non fowler i usually try to fix the problem not the symptom. Heres a pic of the jeep just for fun.

 

Probably some kinda helicoil,They are used when you strip the threads out of a bolt hole and it repairs/replaces it.

 

No. It's an anti-fouler.

 

Yep its an anti-fowler alright.
Remember using them back in the day on one of my smoking beaters.
Surprised they're still in use today.

By the way from the pic, looks like the PO tried the hottest heat range on that plug first before going to that fowler adapter.

If you're lucky there's a remote chance the fouling in that one cylinder might be due to a really bad valve seal.