When you add a linetype to the linetypes library, an item with no defined attributes is added to the list. Once added you can define the new linetype's properties.
To add a linetype to the linetypes library:
Access the linetypes library. How to
Click the Add Item button below
the linetypes list, or right-click in the left pane and select Add
Item. A new entry is added to the list.
Type a name for the linetype and press ENTER.
In the Definition edit box, specify the linetype’s definition. Lines are defined by a series of distances separated by commas. Each number represents the length of either a line segment or space. Positive numbers create a line segment of the specified length. Negative numbers create a space of the specified length. For example, a dashed line may have a definition like 1/4”, -1/4”.
Once you’ve defined the linetype, click OK.