To test the size and taper of component threads along the thread length, L1 & L3 plug gauges and L1 & L2 ring gauges are used in conjunction. Six-step procedure the crest diameter and truncation of the component threads along the crest are checked using crest check plugs and ring gauges.
NPTF are manufactured according to the ANSI / ASME B1.20.5 standards.
ANPT are manufactured according to the SAE AS71051B standards.
NPTF threads do not require a sealant to create a leak-proof connection, hence they are also known as Dry Seal threads.
Additional gauging is required for NPTF and ANPT threads, as the truncation of these threads must be kept within defined ranges.