Radial dimensions measure the radii and diameters of arcs and circles with optional centerlines or a center mark. If the Fit option of the current dimension style is Leader, the dimension is applied with a leader line.
Center marks and lines apply only to diameter and radius dimensions. They are drawn only if the dimension line is placed outside the circle or arc.
The size of the centerline refers to the length of the centerline segments extending from the center mark.
For more information about controlling the location of radial dimension text, see Fitting Text within Extension Lines.