Figure 1-18.--Speclal rules for shop use.
otherwise damaged so that the markings cannot be
read easily. Never use rules for scrapers. Once rules
lose their sharp edges and square corners, their
accuracy is decreased.
SCALES. --A scale is similar in appearance to a
rule, since its surface is graduated into regular spaces.
The graduations on a scale, however, differ from
those on a rule because they are either larger or
smaller than the measurements indicated. For
example, a half-size scale is graduated so that 1 inch
on the scale is equivalent to an actual measurement of
2 inches; a 12-inch long scale of this type is
equivalent to 24 inches. A scale, therefore, gives
proportional measurements instead of the actual
measurements obtained with a rule. Like rules, scales
are made of wood, plastic, or metal, and they
generally range from 6 to 24 inches.
ACME THREAD TOOL GAUGE.--The thread
gauge (fig. 1-19) is used to both grind the tool used to
Figure 1-19.--Acme thread gauges.
machine Acme threads and to set the tool up in the
lathe. The sides of the Acme thread have an included