I have an M5 threaded rod that penetrates a box. Outside it is driven by a motor and it rotates a part inside the box. The box is sealed and I would like to seal the area around the rod as well. I have seen double lip oil seals but I don't think they will work.
The oil is very runny, like water and the reason I am not using a smooth rod (which would be simpler to use in this application) is mainly in order to save on tooling costs as I can get the rods already threaded for very cheap.
If not moving, file the rod down or machine it, and take the smooth rod approach or screw it all way in to head and seal it there..
However, if moving.. I'd say use a nylon bushing smaller than threading and screw it on to the point it will align with edge of box it goes into, if it screws on too easy, it may be a bit too loose cause the friction may unscrew it or you can make it stay using a couple more nuts on each side of the nylon... Then seal the smooth outer edge of the nylon as if just straight rod going through.. The threaded will always work it's way through something so best afix nylon to it, epoxy it, and make it a permanent fixture to the threaded rod and then drill out your hole a tiny bit more.. The only other way I know of would be more costly than just buying straight rods and it involves a type two part joint to isolate inside from outside..