Hi Brian,
you will see from the Autodesk plugin that it
produces facets and I think it then uses the facet
edges to loft thus giving a smooth finish.
I've found given a constant helix and no rotation
you only have to generate enough facets on a small
part of the helix to produce a profile that you can
then sweep to get a screw.
If it was just point contact it's possible to calculate
the profile width from the helix angle bottle width
shaft outer diameter and inner diameter but this
is not what I see in the videos on YouTube.
Cheers
Barry