Coolant out of Engine top?

So we were almost done reconnecting everything after getting an engine rebuild on my 2000 Wrangler TJ 4.0 (manual), then coolant shot out the top of the back of the engine on driver side. There's a hole on the head that looks like a similar size as the fan clutch pulley since one of those bolts turned a little bit before stopping.

I tried so many times to find the head bolt thread pitch since it might be the same, but I couldn't find anything (seems like it should be a quick answer, but no dice)... Any ideas?

Thanks

In the photo, I'm trying to point at the hole with a white zip tie. That's the rear-most fuel injector in the foreground, for context.

 

Could be a coolant temp sensor or miscellaneous bolt?

 

Interesting, I I tried fitting in the old temp sensor we replaced in the thermostat housing to see if it would fit, but it's about twice the diameter that's needed (compared to that other bolt we tried which turned a few times before stopping).

I tried taking closer pics to maybe help:

 

So long story short for anyone still interested, it was for an extra Coolant temp sensor that my TJ doesn't actually have. So after trials and more info, we got a pipe fitting to plug it, and we're up & running to break it in.

I feel really lucky to be part of the wonderful and helpful Jeep community, thank you everyone!