what does nf thread stand for
Best Answer: National fine. This is a series of tap pitches. NC is National Course pitch. The pitch is the distance between the tops of the thread. (M) Just like the distance in the V of the M, the number signifies the number of threads per inch. Threads per Inch is referred to as T.P.I. and the 1/4 value is the Outside most diameter, so the hole to be tapped must therefore be smaller. If one is using a 1/4-28 tap the hole diameter drilled should be .211/.216 diameter.