You can set the outer or inner radius limits for turning operations by picking faces, edges, or points just as you can select faces and points for 3D milling heights.
Choose Selection from the Outer Radius or Inner Radius drop-down menus and pick a suitable face, edge, or point on the model.
Selecting a face for the Inner radius reference on a Turning Profile operation
The resulting toolpath
If a selected face or edge is not concentric about the turning axis, the maximum radius is used.