When i try to make an STL file for 3 D printing, the treads is missing. Anyone that have tryed this and succead ?

Treads?  You building a staircase?  Or did you mean "threads" as one might see on a bolt or a screw?

Yes threads on a bolt.

Are you sure you created the threads correctly?Have you asked your question over at the AutoDesk Discussion Groups > Inventor forum?
John Connor2014-02-05 17:53:50

I have made them true "hole" command and true thread. (Sorry my english, i am from norway.)I have not tryed other forum. Do you know about this ?

I don't use Inventor.