a nurbs circle
When i import 3d file created by catia to rhino, I find:
A degree 5 circle (you can know how to create this circle by the picture below), It’s funy though less use in actual application.

Rhinoceros Tutorials 04 – Piped Ring
Rhinoceros Tutorials 04 – Piped Ring from Jewelturk Net on Vimeo.
Download This Video:
Rhinoceros Tutorials 04 – Piped Ring (English)
http://www.mediafire.com/download.php?myzjj5cif5k
Same Lesson-Rhinoceros Dersler 32 Tel Yuzuk ( Türkçe-Turkish )
http://www.mediafire.com/download.php?gmujyzztknl
making a ring with T-splines
Miguel Gasso recently uploaded a series of uncut videos to YouTube.
In those video tutorials, you can learn how to create a ring with T-splines for rhinoceros. (Be sure you have some experiance on t-splines before watching those tutorials.)
