Ouch that sucks. tRusty had the same thing happen and it was a real bitch to find. I want to say it's 7/8" x14. It's the size of a jam nut only like 1/2" tall and there should be a lock washer. It'll take a 1-5/16" socket, same as the lower ball joint nut on a 1/2ton axle.
You might search for a post by tRustyK5 about it, see if he has any insite on where to find it.