NPT

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Gauge dimensions are as per ASME B1.20.1.
Gauges are supplied as Basic Step & Min/Max Step.
GAUGING EXTERNAL THREADS GAUGING INTERNAL THREADS
With basic step Ring gauge With basic step Plug gauge
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The Basic Step gauge when screwed onto the threads of the component by hand, should be flush with the endof the component face within 1 turn, as shown above.

With Min/Max step Ring gauge With Min/Max step Plug gauge
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When using a Min/Max Step type gauge, the end of the component face should be flush between the Minimum and Maximum steps.

Check the PDF