NATIONAL PIPE TAPERED FUEL (NPTF)
The NPTF is a dryseal thread. The male thread mates with the female thread and a seal is formed when the two are crushed together i.e. threads deformation. Teflon and pipe dope are commonly used when additional sealing is needed. Although this connection is widely used in fluid piping systems, the National Fluid Power Association (NFPA) does not recommend it for hydraulic applications.
NB: Although the NPTF connector and BSPT connector are similar in appearance, the two are not interchangeable.