NPT vs NPTF: Dry-Seal Threads Explained

NPT and NPTF are both 60° tapered pipe threads. NPT is covered by ANSI/ASME B1.20.1, and NPTF (dry-seal) by ANSI/ASME B1.20.5. The difference is that NPTF controls the thread crests and roots so the joint can seal without a sealing compound.

Why NPTF needs more gauge members

Because the crest and root form is controlled, an NPTF thread is checked with L1 and L3 plug gauges and L1 and L2 ring gauges, not only with a basic step gauge.

ANPT

ANPT is the aeronautical variant, covered by SAE AS71051B. It adds a 6-step crest crack check.

Can an NPT gauge check an NPTF thread?

No. The two have different standards and different gauge members, so use the gauge named on your drawing. See our NPT gauges and NPTF and ANPT gauges.