Remind me what this M18 x 1.5 thread piece is again
 

I am drawing a blank at the moment what this M18 x 1.5 thread plug is again. It is not before anyone makes a guess one of the valve cover plugs.

And yes my I-phone camera sucks :/

https://cimg7.ibsrv.net/gimg/rennlis...c66d330c42.jpg
https://cimg4.ibsrv.net/gimg/rennlis...1ec1027c89.jpg
https://cimg5.ibsrv.net/gimg/rennlis...62e32c7719.jpg

99% sure that's not a 944 part, just a universal steel plug.

M18x1.5 also fits the O2 sensor bung.

I'll put my money on it being an O2 sensor plug/bung... If you have just had a wide band installed, it may have been left over from the install?

I only say this... because I found the exact same plug in my glove box and freaked out when I couldn't figure out where it came from

Ha. LOL I am sure you guys are correct now that I think about it........must dig through all my exhaust parts to see where I have a missing O2 sensor.