You can create boss, cut, and surface extrudes from any size surface, face, or plane. The surface or face must be planar. Previously the selection needed to encapsulate the entire sketch.
To extrude from any size planar face:
-
In parts, click Extruded Boss/Base
(Features toolbar) or . This functionality is also available for Extruded Cut 
and Extruded Surface 
.
Select a sketch. Under
From, select
Surface/Face/Plane, and select a planar surface or face, or a plane.