good info here to understand UNF=
http://www.britishfasteners.com/threads/unf.html
but there are probably different versions out there. --
i found this on an AU smiths fan site ;
BA Smiths Temperature Gauge Sender Adaptors
Part No. OD Size ID Size
BA-08N10UNF 1/2” NPT 5/8” UNF Female
BA-0608N 3/8” BSP Male 1/2” NPT Male
BA-1010UNF 5/8” UNF Female 5/8” UNF Male
BA-0375UNF 5/8” UNF Male 3/8” BSP Male
BA-0376UNF 5/8” UNF Male 3/8” NPT Male
BA-0377UNF 5/8” UNF Male 3/8” BSPT Male