I have no idea what thread it is.
the flats (wrench size) measure 18mm across, the threaded stud measures about .510/13mm,
I have no thread gauge that matches... it's somewhere between 18 and 20 tpi and none of my metric thread gauges seem to match.
I do have one though, along with the stud - last summer I bought a couple of steering boxes on eBay trying to find a rebuildable one - no joy, but it has left me with some spare parts
The only way I have to ship it is priority mail because I happen to have a box here and some stamps (I won't go near a post office because of the virus).
Down side is USPS website says $8:30 for postage - if you want to pay the postage, it's yours. Just PM me a mailing address.
Dave