Thermostat Housing bolt size

don't you have the other one to match it up with ?

Go to a hardware store with tho one you already have, they should have a "chart to confirm thread size and diameter

Thermostat is already installed and just started to leak out of where missing bolt is. I'm working on getting the replacement bolt or bolt kit without removing components to get to thermostat housing.

You are making a mountain out of a very simple mole hill. Just match up the bolts and be done with!

So taking car back apart to pull a bolt out is the easiest way you're saying. That would that would make the car undrivable to get replacement bolt. It's drivable now.

You said you lost the other bolt. Is that because it dropped down and the engine caught it? Any access to a flashlight and/or mirror to find it? And if you manage to spot it, any chance that you have a magnet wand to reach in to get it?

Contact a ford dealer parts department and see if they can look up the size of the bolt.

That's sounds like best option to call dealership

1/4x28x1