Figure 6-88.--Measuring threads with a thread micrometer.
come in the same size ranges as ordinary microm-
An explanation of the various methods normally
eters: 0 to 1 inch, 1 to 2 inches, and so on. In
available to you is given in the following paragraphs.
addition, they are available in various pitch ranges.
The number of threads per inch must be within the
Thread micrometers are used to measure the pitch
pitch range of the thread.
diameter of threads. They are graduated and read in
the same manner as ordinary micrometers. However,
Go and no-go gauges, such as those shown in
the anvil and spindle are ground to the shape of a
figure 6-89, are often used to check threaded parts.
thread, as shown in figure 6-88. Thread micrometers
The thread should fit the "go" portion of the gauge,
but should not screw into or onto the "no-go" portion.
Ring and plug gauges are available for the various
sizes and classes of fit of thread. They are probably
the most accurate method of checking threads because
they envelop the total thread form, and in effect,
check not only the pitch diameter and the major and
minor diameters, but also the lead of the thread.
The pitch diameter of a thread can be accurately
measured by an ordinary micrometer and three wires,
as shown in figure 6-90.
Figure 6-90.--Measuring threads using three wires.
Figure 6-89.--Thread gauges.
6-53