Dimension geometry refers to the extension lines, dimension line, arrowheads, and center marks or lines. You control the appearance of these elements of the dimension in the DDIM Geometry dialog box.
You can also set the scale of the dimension sizes, distances, and offsets here. Setting the scale does not affect tolerances, measured lengths, coordinates, or angles.
Modifying Dimension Lines
Modifying Extension Lines
Choosing Dimension Arrowheads
Creating and Modifying Custom Arrowheads