CADtools isometric diameter and radius dimensioning tools work just like the 2D dimensioning tools. Like other dimensions, isometric dimensions are linked to their objects if 'Create live dimensions' is checked in the CADdocument palette.

Isometric Diameter Dimension
To try this tool, first create an isometric circle. Shift-drag a circle in front, side or top view, or create one numerically. Choose the Isometric Diameter Dimension tool. Click on the isometric circle path and drag out to create a dimension. Use the control key to toggle placement of the diameter text. Use the shift key to constrain the dimension to 45 degree increments. Use the alt/option key to create a radius dimension.