Instead of googling everything try cracking open the TMs all the answers are there.
I will help you on this one.
Here is a link that has all the TMs you need to start.
The HMMWV is a 4x4 All-Terrain Military Vehicle introduced by the US Army in 1984 also know as Humvee. With over 300,000 units produced and in active service with 70+ countries as well as in civilian use.
www.nsnlookup.com
Since you have one of the non advanced trucks you would work down the left column, so the first parts TM is
9-2320-280-24P-1
The first thing you want to do is find out your trucks UOC (usable on code) on page 5 you will see the M1097A2 is BVY
Now you look at the TOC and scroll down to Group 05, cooling system,
Then you will see, 0503 Thermostat, water crossover, and attaching hardware and that it is on page 30-1
Click on 30-1 and it will take you to that subject, you will likely have to scroll up a little to see the picture.
View attachment 905788
There you will see the exploded view, pick the number of the item you are looking for and then scroll down to the parts list, we will do #5 the non standard "stud" bolt for the thermostat housing
View attachment 905789
You will see that two #5s are listed "stud, shouldered"
Under the description you will see the UOCs that that part fits, the second one has the UOC of BVY, that is the bolt applicable to your truck.
To the left you will see 4 columns, the second is the NSN number (government part number) and the forth is the manufactures part number.
So now you get on google and search those numbers.
On some fasteners it will give all the information you need, say #10, that is a M10-1.5X35 self locking bolt (that means it is a flanged bolt with serrations to make it self locking.
Now you have all the information to start looking up the parts you need, also download the operators manual and read it from cover to cover and also download the maint. TMs and look up whatever procedures you are doing.
Nobody likes homework but if you do that you will have a MUCH better understanding of what makes your BVY tick!!
Of course there will also be folks here to help if you get stuck.
It is not fair to continue to ask folks to do all the work for you as nobody remembers what size bolts you need and they have to look it up for you.