line that represents an invisible edge on an object

line that used to show and locate the centers of circles and arcs and to represent the center axis of a circular or symmetrical form.

lines used to establish the extent of a dimension

lines capped on the ends with arrow heads and broken along their length to provide a space for the dimension numeral.

thick and used to identify where a view is taken for view enlargements, removed views, or partial views.

thick lines used to identify where a sectional view is taken.

thin lines used in the view of a section to show where the cutting-plane line has cut through material