Various characteristics and features of parts require unique methods of dimensioning.
1.8.1 Diameters. The diameter symbol precedes all diametral values. See Fig. 1-19 and para. 3.3.7. Where the diameter of a spherical feature is specified, the diametral value is preceded by the spherical diameter symbol. See Fig. 3-8 and para. 3.3.7. Where the diameters of a number of concentric cylindrical features are specified, such diameters should be dimensioned in a longitudinal view if practicable.
1.6.2 Radii. Each radius value is preceded by the appropriate radius symbol. See Figs. 1-20 and 3-8 and para. 3.3.7. A radius dimension line uses one arrowhead, at the arc end. An arrowhead is never used at the radius center. Where location of the center is important and space permits, a dimension line is drawn from the radius center with the arrowhead touching the arc, and the dimension is placed between the arrowhead and the center. Where space is limited, the dimension line is extended through the radius center. Where it is inconvenient to place the
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