From FreeCAD Documentation
- Optionally select a circular edge in the 3D view.
- There are several ways to invoke the command:
- Press the Draft Dimension button.
- Select the Annotation → Dimension option from the menu.
- Use the keyboard shortcut: D then I.
- The Dimension task panel opens. See Options for more information.
- If you have not yet selected an edge do one of the following:
- Press E or the Select edge button and select a circular edge in the 3D view.
- Hold down the Alt key, select a circular edge in the 3D view and release the Alt key.
- To position the dimension line do one of the following:
- For a diameter dimension:
- Pick a point in the 3D view, or type coordinates and press the Enter point button.
- For a radial dimension:
- Hold down the Shift key and pick a point in the 3D view.