To Create an Axis Symmetry Line
Using the following procedure, you can create an extension between axis cross hairs showing that the axes are symmetrical about a dimension.
1. On the
Annotate tab, click
Symmetry Line Axis.
2. Select two axes that are perpendicular (normal) to the plane of the screen (shown as cross hairs). To extend the symmetry line to either side, grab a handle of the axis with the mouse pointer and click anywhere outside of the line.