Click the button to the right of the line style in the Properties window to create new line styles. You can add line styles to the palette, remove line styles from the palette, or replace existing line styles in the palette.
Custom Line Dialog
Click the button to the right of the line style to open the Custom Line dialog.
Enter Dashes and Spaces
The Enter dashes and spaces box determines the pattern of the custom line.
As an example, refer to the custom dash line style shown above. A pattern of 0.5, 0.25 will create a line with .5 inch dashes and .25 inch gaps. The pattern repeats the dash pattern and is displayed in the Sample box.
The Sample box shows the new line style.