FreeCAD

Reference external geometry from different body

1. Make the body that requires the external geometry active.
2. Select the desired geometry (e.g., an edge or face) from the other body.
3. Use the “Create shape binder” tool (green blobby icon in Part Design toolbar). This will add a reference to the selected geometry within the active body.
4. You can then use this ShapeBinder object with the “External Geometry” tool within a sketch to create constraints.