1957 D69U

The nuts should be 1B4206 which has been replaced with 6B6683. My local Cat dealer has them in stock so I assume most dealers will have them. You are correct the nuts are grade 8 UNF but other than that there is nothing special about them.

Try McMaster Carr

Here's what I could find for specs....plain hex nuts....
1B4206
  [attachment=66407]1B4206 plain hex nuts.JPG[/attachment]

6B6683
[attachment=66408]6B6683 plain hex nuts.JPG[/attachment]

Thanks for the info, the transmission is going in Saturday. Rolling the dice on this one. Bought the tractor missing the transmission and without hearing it run. Sometimes ya just have to have faith.
My ace up the sleeve will be Tractor Don watching over my shoulder. Good times!

Well if Don is supervising the operation, you should be in good hands. That doggone guy is always busy wrenching, fishing or chasing ladies to work on any of my tired iron.
Please feel free to share some photos and progress reports.It is nice to visualize and learn from another's handiwork. JM

Juiceman, they got it installed, I was a good supervisor. I didn’t do anything😁 I might do a little wrenching and a little fish’n but I need to borrow your shop manual for women because I can’t fix them 😳🤣
Can’t seem to load pics. I don’t have a problem anywhere else🙄

So today after several evenings of work the D6 did fire up and drive quite well. An oil change and a few adjustments remain. Before we take it home I plan to hitch up a big disc and put her to work in the field to be sure it does not get hot and to work out any kinks that arise. This project has been a testimate to the knowledge and generosity of our caterpillar community as well as a great family project. The story begins with a friend of a friend (Austin) that knows of a D6 about to be scrapped. It was owned by a woman whose husband had died. It was apart and now missing pieces. On Austin’s word that it had been a runner, I bought the tractor unseen. Another deal was struck with Louis the uncle of another friend for many of the missing parts including the transmission. I retrieved the remaining parts several days after Louis’s passing. I was steered onto another local cat guy (Dustin) that offered up some of the other missing parts. Don’s bucket of bolts and trinkets provided greatly. A day trip to the cat dismantlers in Fresno for ujoints and misc parts and the only things missing now are the front floor plates and the forward / reverse lever. It took a village to get this project done. I guess that is what makes Cat people special. Thank you my friends on ACMOC, my new friends, my old friends, and my friend that passed.

That is neat! Glad you managed to acquire all of the parts via networking. Some tractors can be challenging to find "all" the parts needed, call it a scavenger hunt of sorts...
Let's see some action photos and testimony of how great those D6s are! JM