Creating Solids and Surfaces from 2D - Autodesk AutoCAD 2013 Practical 3D Drafting and Design - page 93

Note
Instead of using this option, I advise you to apply the SWEEP com-
mand, which provides greater flexibility and better results for complex
geometry.
• Taper angle : This option allows you to create an extrusion object with an
angle applied to the vertical faces. It prompts you for the taper angle and
height. If the angle is positive, sections decrease; and if negative, sec-
tions increase. If the taper angle or height values are too large, a vertex
or edge may be reached before the specified height.
EXTRUDE applied to faces and edges
If we press the Ctrl key, AutoCAD allows us to select the vertices, edges, and faces
(called subobjects) of solids and surfaces.
So, we can apply EXTRUDE to edges and faces. When prompting for the selection,
we press the Ctrl key and select these subobjects. Then, we continue the command
by typing the height value or apply another option. The new objects are independent
of the old ones.