That's a little odd.
'3,4,5,6,7,8...' would seem to indicate M3, M4, M5, etc. metric taps.
But NC/NF mean National Coarse and National Fine, i.e. non-metric threading standards.  e.g. 1/4"-20 is a common NC threading, and 1/4"-28 is an NF threading.

M5, M6, M8 taps are the generally useful taps for bike frames IIRC.  M5 is water bottle bosses.  I think brake cable adjusters are M6.  Derailer hanger threads are in the neighborhood of M8.

BB threads are a specialized thing, i.e. you have to buy taps made specifically for the bike industry.

Ethan
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