To Create Diameter Dimensions
To Create a Diameter Dimension for an Arc or a Circle
1. Right-click and choose Dimension from the shortcut menu or click > 
Normal.
Normal.2. Double-click the arc or circle.
3. Middle-click to place the dimension. The dimension is created.
To Create a Diameter Dimension for a Revolved Section
1. Right-click and choose Dimension from the shortcut menu or click > Normal.
Normal.2. Select the entity to be dimensioned.
3. Select the centerline that will be the axis of revolution.
4. Select the entity again.
5. Middle-click to place the dimension. The dimension is created.