From FreeCAD Documentation
- Select Pocket in the Tree view.
- Click
Mirrored:
- The Mirrored parameters task panel opens.
- Select Plane Vertical sketch axis
from the pulldown menu. The plane will be defined by this axis (the Y axis) and also by the Z axis of the sketch. Note that selecting Base YZ Plane would have the same result.
- Click OK.
- You should now have a part that looks like Fig: CC5.