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4.5.2 Dimension number

Usually, it is recommended that dimension number should be written with 2H or
HB pencil and the height should be between 2.5 – 3.0 mm. The number should be

placed about 1 mm above and at the middle of a dimension line as shown in figure

below :

Figure 4.13 : Good dimensioning practices

4.5.2.1 Number system

There are some rules that need be followed on the way to write dimension. It can

be divided into three number systems :

Metric system
12, 12.5, 12.55, 0.15 (not .15) etc
ISO and JIS standard

Decimal-inch system
0.45 (not .45), 9.275 etc.
ANSI system

Fractional-inch 4 2
, 5 .
system 5 3

Figure 4.14 : Number system for dimensioning