To Set the Default Representation for Diameter Dimensions (AutoCAD Mechanical Toolset)

1. At the Command prompt, enter AMOPTIONS.
2. In the Options dialog box, click the AM:Standards tab.
3. In the Standard Elements list, double-click Dimension. The Dimension Settings dialog box appears.
4. Click Diameter. The Diameter Representation dialog box appears.
5. Select the check boxes corresponding to the behaviors to enable. The preview updates.
6. Click OK until all dialog boxes close.