2 things… The stringing? and the bigger concern, why isn’t it printing the part as shown on the screen? This part was created in Inventor 2016 using the plugin CoolOrange to do the threads. Exported as an STL to ReplicatorG 0400. Scaled by 10. Then generated gCode using Skeinforge 50. See pictures…
I can’t really tell from the picture, but it looks like the part was originally designed to have 3 “fins” instead of a flat surface and 3 grooves? In that case, my best guess is that it’s an object manifold issue, and your slicer’s attempt to fix it resulted in a reversal of the solid fins and empty space.
the stringing I would say is actually quite minor. You could easily remove that with an exacto knife (aka. scalpel). If you really want it gone, try decreasing the extrusion temperature slightly, 5°C for starters and/or increase the retraction distance slightly (fractions of a mm to start with).
For the CAD-product difference I would suspect either an export error or a problem in the slicer. I don’t know any specifics about the software you are using, but I had similar issues when there were auxiliary construction planes present when working with Solidworks. If you are using similar things, try hiding them, then export the file to stl again. Alternatively, try using the automatic repair in netfabb to fix this. There should be numerous tutorials on this on the interwebs
If that doesn’t work, try a different slicer. Cura is an open source option that I like to use.
We are having the exact same issue. We actually printed a couple parts using the exact same method, but the latest part fills the hole. Even in the .stl file preview the part is unfilled. Did you ever figure it out?