Gauges for Taper Pipe Threads  NPT

NPT specified in American standard ( ANSI ) are used to connect pipes, plumb parts, fluid equipments ,etc and are purposed to increase the density resistance of the threaded parts .
Gauges for taper pipe threads ( NPT ) are used for measuring dimension of such the threads.

There are many types of gauges for taper thread ( NPT ) with various different notches . In general, the gauges for taper threads L1 having 3 - steps notches , ie. minimum limit position 1, basic position B and maximum limit position  2 , are the most commonly used. The use of the taper thread gauges has been explained in the previous pages .
However, since there is a specification of truncation for major & minor diameters of thread height , it is recommended to measure major and minor diameters using plain taper gauge having 6-step notches .
First, the pitch diameter of the taper thread is measured with a taper thread gauge. For example, when it is judged pass at near the notch of basic position  B .  then for major and monor diameter, is also similar . There is the item is judged pass when the pipes can go within limit range of B .