Spark plug strange question
 

I was changing plugs on my 912 engine today. I purchased it a few months ago and have been building it up from a long block. Everything has been going well except when I was changing one of the plugs, it looked like there was a spring inserted in the thread of one of the plug holes. My guess is that one of the PO stripped the thread and had to somehow rethread the hole. Is this a good guess? Should I be scared?

Looks like you found a helicoil in that plug hole.

This is not uncommon at all and nothing to worry about.