Extension lines are used to extend dimensions beyond the outline of a view so that they can be read easily. These thin, unbroken lines are started about one sixteenth of an inch from the outline of the object and extend about one eighth of an inch beyond the outermost dimension line. They are drawn parallel to each other and perpendicular

Figure 3-28.-Correct and incorrect procedures for draw- ing a hidden edge line that intersects a visible edge line.

Figure 3-29.-Correct and incorrect procedures for draw-ing intersecting hidden edge lines that are on different levels.

to the distance to be shown. (See fig. 3-30.) In unusual cases, extension lines may be drawn at other angles if their meaning is clear. As far as practical, avoid drawing extension lines directly to the outline of an object. When it is necessary for extension lines to cross each other, they should be broken, as shown in figure 3-31.