44 Chapter 3
Dimension Lines.
Dimension lines are solid lines similar in weight to extension lines that are used to indicate length. They
are drawn from one extension to the next, representing the distance between the extension lines. Once
the external shape and internal features of a part are represented by a combination of lines, further in-
formation is provided by dimensions. Fractional, decimal, and metric dimensions are used on drawings
to give size descriptions. Each of these three systems of dimensioning is used throughout the text.
Dimension lines are fine lines that are often broken at the dimension and ending with arrowheads,
dots, or a small diagonal line (Figures 3.6, 3.7A and B). The tips or points of these arrowheads indicate
the exact distance, referred to by a numerical dimension placed either at a break in the line or directly
above the lines near their center.
Figure 3.5A Center lines indicate the centers of circles, arcs, and symmetrical objects.