Difference Between NPT and NPTF
http://www.differencebetween.net/technology/difference-between-npt-and-nptf/
WEBNPTF, or National Pipe Taper Fuel, is a dryseal tapered pipe thread, which is kind of a modified NPT thread but provides better seals than NPT threads. The ‘f’ in NPTF refers to fuel and as the name suggests, it is derived from NPT and even shares the same diameter, taper shape, and threads per inch with NPT.
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