To take a measurement with a common rule, hold
the rule with its edge on the surface of the object being
measured. This will eliminate parallax and other errors
that might result because of the thickness of the rule.
Read the measurement at the graduation that coincides
with the distance to be measured, and state it as being
so many inches and fractions of an inch. (See fig. 2-2.)
Always reduce fractions to their lowest terms, for
example, 6/8 inch would be called 3/4 inch. A hook or
eye at the end of a tape or rule is normally part of the
first measured inch.
Bolts and Screws
The length of bolts and screws is best measured by
holding them up against a rigid rule or tape. Hold both
the rule and the bolt or screw to be measured up to
your eye level, so that your line of sight will not be in
error in reading the measurement. As shown in figure
2-3, the bolts or screws with countersink-type heads are
measured from the top of the head to the opposite end,
while those with other types of heads are measured
from the bottom of the head.
Outside Pipe Diameters
To measure the outside diameter of a pipe, you
should use some kind of rigid rule. A wooden rule or
a steel rule is satisfactory for this purpose. As shown in
figure 2-4, line up the end of the rule with one side of
the pipe, using your thumb as a stop. Then, with the
one end held in place with your thumb, swing the rule
through an arc and take the maximum reading at the
other side of the pipe. For most purposes, the
measurement obtained by using this method is
satisfactory. It is necessary that you know how to take
this measurement, as the outside diameter of pipe is
sometimes the only dimension given on pipe
Figure 2-3.Measuring the length of a bolt or screw.
Figure 2-4.Measuring the outside diameter of a pipe.
Inside Pipe Diameters
To measure the inside diameter of a pipe with a
rule, as shown in figure 2-5, hold the rule so that one
corner of the rule just rests on the inside of one side of
the pipe. Then, with one end thus held in place, swing
the rule through an arc and read the diameter across the
maximum inside distance. This method is satisfactory
for an approximate inside measurement.
Figure 2-5.Measuring the inside diameter of a pipe.
Figure 2-2.Measuring with and reading a common rule.