Hi Terry, Given what the others have said I assume you have a serious need rather than just a cosmetic one or that the need for cosmetic outweighs the overhead.
In my case as I was preparing a small part for diecasting I needed all the detail. I made a helical sweep based on the OD of the thread and the pitch. I left the sketched section (which I sketched from Machinery's Handbook) parallel to the sketch plane rather than normal to pitch as that is the way all thread systems are defined as far as I know. The sketch could use a saved sketch if reuse is an issue. I used the centre of the thread depth as the section centre but it could be offset. I also gave the thread run out buy adding a tan arc at the head end (vary the R value for the run out ramp). You can vary the shape of the run out but it must get clear of the OD by more than the thread depth. You can use a revolved surface and solidiy or just a solid cut. The surface comes into its own when you have the case that your thread runs pretty much up to a flange (e.g. head) of the part in which case some surface modelling is required to trim the helical sweep so it does not intersect the flange.
Not too tricky. Hope this helps.
Regards, Brent Drysdale Senior Mechanical Designer Tait Radio Communications New Zealand DDI +64 3 358 1093 www.taitradio.com