Machining Fundamentals
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4.1.1 Reading the Rule (US Conventional)
A careful study of the enlarged rule section will
show the different fractional divisions of the inch
from 1/8 to 1/64, Figure 4-4. The lines representing
the divisions are called graduations. On many rules,
every fourth graduation is numbered on the 1/32
edge, and every eighth graduation on the 1/64
edge.
To become familiar with the rule, begin by mea-
suring objects on the 1/8 and 1/16 scales. Once you
become comfortable with these scales, begin using
the 1/32 and 1/64 scales. Practice until you can
quickly and accurately read measurements. Some
rules are graduated in 10ths, 20ths, 50ths, and
100ths. Additional practice will be necessary to read
these rules.
Fractional measurements are always reduced to
the lowest terms. A measurement of 14/16″ is
reduced to 7/8″, 2/8″ becomes 1/4″, and so on.
4.1.2 Reading the Rule (Metric)
Most metric rules are divided into millimeter
or one-half millimeter graduations. They are
Millimeters (mm) Centimeters (cm)
Half millimeters
(0.5 mm)
Metric
Fractional inch
Decimal inch
Figure 4-2. Compare the metric (millimeter-graduated) rule with
the more familiar rules graduated in fractional and decimal inch
units.
Figure 4-3. Many different types of rules are used to make measuring quicker and more accurate. (L. S. Starrett Co.)
6” steel rule
Rule with adjustable hook
Narrow rule
Small rule with holder