I think I misunderstood you. Are you trying to use a lead screw or M8 threaded rod with a coupling nut?
If you are talking about a lead screw, you could try this thing along with a lead screw nut, but I have no idea if it would work since the designer hasn’t even tried it: http://www.thingiverse.com/thing:1727299
(On that note, I can’t find a M8-1.0 coupling nut. I would just buy threaded rod that is M8-1.25, or stick with 5/16.)