steering pinion arm nut

[easyrider]

I just received my power steering box and I noticed that it didn't come with a pinion arm nut, so I called and they told me to use my old nut. My old nut was on my manual steering box and is not the same size. So, I started to look for another one for this application and no one knows the size or thread of the nut. the old one I think was 7/8x14 but it won't start on my out put shaft. Did anyone else have this problem? If you had to purchase a pinion shaft nut, what size was it and where did you get it? Thanks for the help!