At the start of a project, you load the linetypes that are required for the project so that they are available when you need them.
If you want to know what linetypes are already available, you can display a list of linetypes that are loaded in the drawing or stored in an LIN (linetype definition) file.
This program includes the linetype definition files acad.lin and acad.lin. Which linetype file is appropriate depends on whether you use imperial or metric measurements.
Both linetype definition files contain several complex linetypes.
If you select a linetype whose name begins with ACAD_ISO, you can use the ISO pen-width option when you plot.
You can remove unreferenced linetype information with PURGE or by deleting the linetype from the Linetype Manager. BYBLOCK, BYLAYER, and CONTINUOUS linetypes cannot be removed.