the basics about how to use a national pipe gauge

      It's really easy for Using National Pipe Gauges (NPT, NPTF, NPS), if the Go thread plug for NPS (straight) goes in to the threaded hole or  the NoGo does not, then the product is usually considered within Allowable range oracceptable.This is very simple about the use of  NPT or NPTF or ANPT gages，because you only have 1 primary L1 gauge/gage that as both Go and NoGo using the gauge notch(s) or ring face to line up with the end of the product thread +/_ （the allowable tolerance） the basic thread form is within promise.  Of course with NPTF and ANPT the complexity increases that  when the L2/L3 is called for to determine compliance to a wrench tight position and thread taper.