Hi Scott,

Gearotic may be able to generate those profiles.

But an easier method would be to modify a STEP file from McMaster-Carr like this one:

https://www.mcmaster.com/3684N11/

Regarding STL to STEP conversion: that's not a file format conversion; it's going from geometry made up of flat triangles to geometry represented by smooth curves. Doing it right is pretty complicated and is likely to create accuracy issues.

- Peer