Diameter dimension
Use the CAD circle tool to create a circle in scale. Select the Diameter dimension tool. Click and drag to position the diameter dimension. Hold down the shift key to constrain the dimension appearance to 45 degree angles. Hold down the control key to toggle the placement of the diameter dimension text. To place the diameter symbol in front of the dimension, check the box inside the CADtext palette.

Radius dimension
This tools works much like the previous tool. Use the CAD circle tool to create a circle in scale. Select the Radius dimension tool. Click and drag to position the radius dimension. Hold down the shift key to constrain the dimension appearance to 45 degree angles. Hold down the control key to toggle the placement of the radius dimension text. To place the radius symbol in front of the dimension, check the box inside the CADtext palette.