3D Primitives and Conversions - Autodesk AutoCAD 2013 Practical 3D Drafting and Design - page 144

3. With the UCS command, create a user coordinate system aligned with the
front facade. The origin is the lower-left corner of the first box, the X axis
defined by the other lower corner, and the XY plan defined by one of the
top corners of that face. This UCS also allows us to control the precise
position of the torus.
4. Applying the TORUS command, pause over the midpoint on the lower
edge, point along Y, and write 30 . The Otrack function must be on.
Another way is to specify the torus origin at 20,30 absolute coordinates.
The radius of the torus is 11 and the radius of the section is 1.5 .