Tool

Pipe Thread Finder

Enter the size and the threads per inch (or the pitch). See which pipe threads it could be: NPT, R/Rc, Rp or G.

55° vs 60°

R, Rc, Rp and G (old JIS: PT, PS, PF) are 55°, with rounded crests and roots.
NPT is 60°, with flat crests and roots.
With different angles, the flanks cannot lie flat against each other. NPT does not mix with any of them.

Before you trust the result

Taper or parallel: measure the crest diameter on the first, fourth and last full threads.
In 1/2 and 3/4, a trial fit proves nothing. Measure the thread angle.
Confirm with a thread gauge from the right system.

Reference

Size	PT / PF (55°) threads per inch	Pitch	NPT (60°) threads per inch	Pitch	Note
1/8	28	0.0357 in (0.907 mm)	27	0.0370 in (0.941 mm)
1/4	19	0.0526 in (1.337 mm)	18	0.0556 in (1.411 mm)
3/8	19	0.0526 in (1.337 mm)	18	0.0556 in (1.411 mm)
1/2	14	0.0714 in (1.814 mm)	14	0.0714 in (1.814 mm)	Same pitch
3/4	14	0.0714 in (1.814 mm)	14	0.0714 in (1.814 mm)	Same pitch
1	11	0.0909 in (2.309 mm)	11.5	0.0870 in (2.209 mm)

Table 2 from the article PT, PF and NPT: Reading Old JIS Pipe Thread Callouts. All data on this page comes from that article.

This is general information, not engineering advice. Thread standards are revised; check the edition named on your drawing, and confirm gauging requirements with your own quality department.

If you are sourcing a turned part with pipe threads, send the drawing.