Thick Lines in AutoCAD require a linetype name.
The ByBlock linetype displays objects with Continuous linetype until the objects are combined into a block definition.
The ByLayer linetype displays objects with the linetype assigned to the current layer. The continuous linetype displays objects with a solid, unbroken pattern. Linetypes can be a pattern of dashes, dots, text, and symbols or unbroken and continuous.
The AutoCAD software package comes with a library of standard linetypes that has 38 different standard linetypes.
