26 GD&T: Application and Interpretation
Copyright Goodheart-Willcox Co., Inc.
a space were used, the symbol and number may
appear detached. Past drawing practice used the
abbreviation DIA following the dimension value.
Zeroes should not have a line drawn through
them to differentiate them from the letter O. A line
through a zero can cause it to be mistaken for a
diameter symbol.
A spherical diameter symbol includes the
letter S preceding the diameter symbol. The sym-
bol is placed in front of the dimension value of the
sphere. See Figure 2-4. There is no space between the
S and the diameter symbol and no space between
the diameter symbol and the dimension value.
The abbreviation R is used as the radius sym-
bol. The R precedes the numeric radius value. See
Figure 2-5. A space should not be shown between
the symbol and number because the symbol
would appear detached. Prior to the release of
ANSI Y14.5M-1982, standard practice applied the
letter R as a suffi x to the radius dimension value.
A controlled radius symbol is specifi ed using
the abbreviation CR as a prefi x to the dimension
value. It is applied in the same manner as the R
symbol but includes a more exacting requirement
on the feature surface.
Figure 2-5 shows two radius dimensions
applied to the same surface. One has the R symbol
and the other has the CR symbol. Both are applied
in this fi gure to show the similarity in applica-
tion. On a drawing or model, only one of the two
dimensions would be applied based on the desired
requirement for that surface.
A spherical radius symbol is indicated by
the letters SR preceding the dimension value. No
space is placed between the two letters. See Fig-
ure 2-6. No space is shown between the letters and
dimension value because the letters and numbers
would appear detached.
Counterbores and spotfaces were, in the past,
indicated by the same symbol, but they are now
indicated by different symbols. The counterbore
symbol is shaped like the bottom of a counterbore.
See Figure 2-7. The counterbore symbol precedes
the diameter symbol and the numerical value rep-
resenting the diameter of the counterbore. In the
given fi gure, the counterbore diameter is followed
by the depth symbol.
Depth may be specifi ed in a dimension nota-
tion by placing the depth symbol in front of the
depth value. The depth symbol is a downward-
pointing arrow that extends from a horizontal line.
See Figure 2-7. To avoid confusion, the depth sym-
bol should not be placed too close to the dimension
value that precedes it.
The spotface symbol is similar to the coun-
terbore symbol except that it includes the letters
SF inside the symbol, as shown in Figure 2-8. The
spotface symbol is followed by a diameter symbol
Drawing
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Drawing
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Figure 2-4. A spherical diameter is indicated with an S
placed in front of the diameter symbol.
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Figure 2-5. The radius or controlled radius symbol
precedes the number.
Drawing
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Figure 2-6. A spherical radius is indicated with an SR
placed in front of the number.