Understanding Line Types 45
Different types of arrowheads are used in dimensioning. The point or tip of the arrowhead touches
the extension line. The size of the arrow is determined by the thickness of the dimension line and the
size of the drawing. Closed and open arrowheads are the two shapes generally used. The closed arrow-
head is preferred. The extension line usually projects 1/16 inch beyond a dimension line. Any additional
length to the extension line is of no value in dimensioning.
When dimensions can be added together to come up with one overall dimension, they are known
as chain dimensions. Chain dimensions are usually expressed in a single line whenever possible
(Figure 3.7B).
Figure 3.5B Center lines indicate the centers of circles, arcs, and symmetrical objects.