Pipe Circumferences
To measure the circumference of a pipe, you must
use a flexible-type rule that will conform to the shape
of the pipe. A fabric or steel flexible tape rule is
adaptable to this job. When measuring the pipe, make
sure the tape is wrapped squarely around the axis of the
pipe to ensure that the measurement will not be more
than the actual circumference of the pipe. This is
extremely important when you are measuring a large
diameter pipe.
Hold the rule or tape as shown in figure 2-6. Take
the reading, using the 2-inch graduation, for example,
as the reference point. In this case the correct reading
is found by subtracting 2 inches from the actual
reading. In this way the first 2 inches of the tape,
serving as a handle, will enable you to hold the tape
securely.
Inside Dimensions
For an inside measurement such as the inside of a
box, a folding rule that incorporates a 6- or 7-inch
sliding extension is one of the best measuring tools. To
take the inside measurement, first unfold the folding
rule to the approximate dimension. Then, extend the
end of the rule and read the length that it extends,
adding the length of the extension to the length on the
main body of the rule. See figure 2-7. In this illustration
the length of the main body of the rule is 13 inches,
and the extension is pulled out 3 3/16 inches; the total
inside dimension being measured is 16 3/16 inches.
Figure 2-6.—Measuring the circumference of a pipe with a
tape rule.
Figure 2-7.—Using a folding rule to measure an inside
dimension.
Notice in the circled inset in figure 2-8 that the
hook at the end of the particular rule shown is attached
to the rule so that it is free to move slightly. When an
outside dimension is taken by hooking the end of the
rule over an edge, the hook will move to locate the end
of the rule even with the surface from which the
measurement is being taken. By being free to move, the
hook will retract toward the end of the rule when an
inside dimension is taken. To measure an inside
dimension using a tape rule, extend the rule between
the surfaces as shown, take a reading at the point on the
scale where the rule enters the case, and add 2 inches.
The 2 inches are the length of the case. The total is the
inside dimension being taken.
Outside Dimensions
To measure an outside dimension using a tape rule,
hook the rule over the edge of the stock. Pull the tape
out until it projects far enough from the case to permit
measuring the required distance. The hook at the end of
the rule is designed so that it will locate the end of the
Figure 2-8.—Measuring an inside dimension with a tape
rule.
2-3
