Frequent contributor Michael Partenheimer notes that the National CAD Standard (NCS) no longer associates a color to a plot thickness. He has submitted three separate but related LISP routines to help AutoCAD users with this transition. The first, Color2lineweight.lsp, is designed to set the lineweight of each layer based on the layer color. It only contains mappings for colors 1–19, so you can use this as a guide for setting up a routine that fits your layer colors. The second routine, NCSpstyle2lineweight.lsp, sets layer lineweights based on the layer plot styles in STB plot style–based drawings. The last routine, Lineweight2Color.lsp, sets layer colors based on the lineweight of that layer.
All of these LISP routines are currently configured to be loaded and executed by dragging and dropping them into AutoCAD. If you prefer to load these routines up front and execute at a later time, you can do so; instructions are provided in each file.