I built joes2006 as well. I used 1/2-8 2 start. This gives 4 tpi. Lots of the builders of Joes 4x4 have used the 1/2-10 5 start, which gives 2 tpi. I think that will work on the 06 and am looking into getting some, but don't have any yet.
I can tell you that the 1/2-8 2 start works well.