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Exploring Drafting
millimeter, a zero does not follow the last
digit to the right of the decimal point.
125.5, not 125.50
Where some millimeter dimensions are shown
on an inch-dimensioned drawing, the symbol
“mm” follows the millimeter values.
Note
Tolerancing
The foundation of modern manufacturing
is the ability to produce numerous parts, all
of which meet the exact specifi cations for
assembly or use. In reality, it is impossible to
make a part to its exact dimensions. Tolerancing
allows manufacturers to control the precision
and quality of the parts they make. A tolerance
is an allowable variance from the original
1. When a millimeter dimension is a whole
number, the decimal point and following
zero are not shown. This holds true
unless tolerances are shown.
125, not 125.0
2. When a dimension is less than one
millimeter, a zero is shown to the left of
the decimal point:
0.5, not .5
3. All metric drawings should be clearly
identifi ed as such. The symbol for
millimeter (mm) should not be added
to every dimension. Instead, the
drawing should have a note stating
“UNLESS OTHERWISE SPECIFIED, ALL
DIMENSIONS ARE IN MILLIMETERS.”
4. A space (or comma) is not used to separate
digits for dimensions into groups:
20500, not 20 500
5. When the dimension exceeds a whole
number by a decimal fraction of one
Goodheart-Willcox Publisher
Figure 10-37. When parts are designed to conform to different standards of measurement, the drawing may be
completed without dimensions. Except for the thread size, no dimensions are shown on this master drawing. After
the print is made, dimensions in either inch or metric units are added.
Copyright Goodheart-Willcox Co., Inc.