Object Line
A heavy solid line used on a drawing to represent the outline of an object.
Hidden Line
A line type that represents an edge that is not directly visible, because it is behind or beneath another surface.
Center Line
A line consisting of a long dash followed by a short dash that is used to show and locate centers of arcs and cricles, and to describe the center axis of cylindrical forms
Phantom Line
A line used to show the alternate positions of an object or matching part without interfering with the main drawing.