I was going to change my thermostat today and rounded off the top thermostat bolt. I think I could probably get vise grips on it and get it out but I don’t know what size/part number I need to replace it. Any help would be appreciated. It’s a 2011 f150 5.0 by the way.

 

This is what I would suggest,

There had to be more than one bolt holding the housing in place.
If you could provide the numbers on the head of the remaining bolt(s) and the measurement of the diameter and length in inches, I should be able to come up with a spec for what is most likely a metric size bolt and have the info to be pretty sure and hopefully save you some trouble.
What size socket did you use to remove the other bolt(s)?

Here is something that might get you out of the woods until you obtain a replacement. If you have a hacksaw,saw a slot in the head of the problem bolt once you get it out,That way you can reuse it until you get a replacement , Only saw the slot deep enough to tighten that bolt with a screwdriver. Can you do this?

 

Thanks for the response I was able to get it figured out the part number was W713197S437