To Create a Diameter Dimensional Constraint (AutoCAD Mechanical Toolset)

1. In the Authoring Palettes window, in the Dimensional tab, click Diameter.
2. Select an arc or a circle object.
3. Specify the dimension line location.
4. In the dimension text, specify a name for the dimensional constraint, to the left of the "=" sign.
   Note: The dimension text of the form “name=value
5. Enter a value or specify an expression to the right of the "=" sign.
   Note: If you specify an expression, it is local to the view you are editing. To make it valid across all views, add the dimension to the Family Table as a calculated column and specify the expression in the column properties.
6. Press Enter.