Chapter 3 Datums 107 When two cylindrical features of different diameters are used to establish a datum axis, then the datum target points are identified in correlation to the adjacent cylindrical datum feature. Refer to Example 3-34. Example 3-34. Two cylindrical features of different diameters used to establish a datum axis. Example 3-35. Establishing datum axes with a cylindrical datum target area and a circular datum target line. Cylindrical datum target areas and circular datum target lines can also be used to establish the datum axis of cylindrical shaped parts, as shown in Example 3-35. In this application, the datum target area is a designated width band that goes all around the part. This datum target area is shown as two phantom lines with section lines between. The datum target line is a phantom line that goes all around the part.