npt threads

There are many tutorials on how to model threads from scratch but what you would have to do is create a tapered helix as your loft part. What I usually do to have actual 3d thread is to take a part from mcmastercarr.com and use it as a tool to make the thread. If your making a tapped hole get a model of a bolt (in this case some sort of pipe fitting that has your thread) then insert->part and locate it with the available mates, place it where you want the actual screw to go in. If you already made a hole make sure it is smaller than your bolt so you can use the subtract feature. To use subtract go to feature->insert feature->combine and then choose subtract. This way your using the bolt model as a "tap" to make your threads for you.