Spark plug issue

[windydubber]

Hi all,
Please bare with me. I'm not a mechanic. Just keen to do as much myself as possible.
Today I tackled the so called easy stuff. Air filter change. No problem. Dizzy cap. No problem. Hat Leads. No proble. Rotor arm. Couldn't shift??? But it was the spark plugs that had me. Three came out and were replaced no problem. But the one closest and to the right was a bugger. First of all buried in the tinware. Then after half a hour of trying to get the new one in realised the one I took out had a smaller thread???? Am I being stupid? This isn't normal is it? Does this mean someone has threaded it in the past and done a repair???
Anyway I put the old plug back in for now. Any suggestions welcome.
Cheers

[kevtherev]

Does this smaller have any identification marks?

[windydubber]

I had to put it back in so the van runs. It was weird though as the thread is smaller for the first half of the thread then about 2-3 mil thicker??

[kevtherev]

I had to put it back in so the van runs. It was weird though as the thread is smaller for the first half of the thread then about 2-3 mil thicker??

OK so what was the number/letters on the plug you removed?

[itchyfeet]

Next time take pictures, a picture says a thousand words, just about everybody has a digital camera, would have saved you taking it out again to read the number and told us alot about the strange thread.

[windydubber]

I know I should have taken pics. However all I had was my iPhone and very oily hands so didn't want to mess the phone up! Lol.

[itchyfeet]

Vans worth more than a phone and oil wipes off

[bigherb]

Yep a pic would help but is sounds like the thread has been repaired with a helicoil or insert and part has come out with the plug or someone has fitted an insert that uses a 12mm spark plug.