When you import a file and explode it in Revit, the import lines are converted to model lines. If this is not the line type you want to work with, you can use the Convert Lines tool to convert model lines to detail lines. Then, using Convert Lines, you can convert the lines back to their original line type. In families, you can convert symbolic lines to model lines, and vice-versa.
Convert Lines is also useful if you want to convert lines that were mistakenly drawn as the wrong line type. During conversion, Revit remaps the styles of, and references to, the lines being converted. See Exploding Imported Geometry for more information about importing files into Revit.
To convert a line type