2 Alphabet of LinesThe different lines and line symbols used on drawings form a kind of graphic alphabet commonly known as the alphabet of lines. Two line widths-thick and thin-are generally used. Drawings are easier to read when there is good contrast among different kinds of lines. All lines must be uniformly sharp and black.
3 Visible Object LinesVisible Object Lines are thick dark solid (unbroken) lines that are used on drawings to indicate the edges and details of an object.
7 Center LinesCenter lines are thin lines made up of alternating long and short dashes. They are used to indicate the center of symmetrical features, such as circles or arcs. They are used as an aid in dimensioning.
11 Dimension, Extension & Leader Lines Dimension, Extension and Leader Linesare thin lines used for dimensioning purposes. Dimension and leader lines generally end with arrow heads and are accompanied by a number indicating a size or location dimension.
13 Cutting Plane LinesCutting Plane or Viewing Plane Lines are very thick lines that indicate where an imaginary cutting plane passes through an object, for viewing or sectioning purposes. Arrowheads on both ends of the line point toward the surface to be viewed.
15 Break LinesBreak Lines are used to shorten a view, or to eliminate repetitive details when an entire view is not necessary. Short break lines are thick wavy freehand lines. Long break lines are thin straight zig-zags.