I hope this will help you.
Unified class 1A/1B series. Class 1 fine thread series (NF-1) is approximately equivalent dimensionally to Unified class 2A/2B series. Standard Unified series threads should be considered prior to approval of replacement by non-standard threads.
b. American National class 2 coarse thread series (NC-2), 8 thread series (9N-2), 12 thread series (12N-2), 16 thread series (16N-2), and extra fine series (NEF-2) are most nearly equivalent to Unified series UNC-2A/2B, 8UN-2A/2B, 12UN-2A/2B, 16UN-2A/2B and UNEF-2A/2B, respectively. Class 2 fine thread series (NF-2) is approximately equivalent dimensionally to Unified class 3A/3B series, but the use of class 2A/2B series should be considered prior to approval of replacement by class 3A/3B.
c. American National class 3 series NC-3, NF-3, NEF-3, 8N-3, 12N-3 and 16N-3 are most nearly equivalent to Unified class 3 series UNC-3A/3B, UNF-3A/3B, UNEF-3A/3B, 8UN-3A/3B, 12UN-3A/3B, and 16UN-3A/3B, respectively.
d. There is no Unified thread class equivalent to the old American National class 4 which required selective fit of parts due to the possibility of interference.
c. American National class 3 series NC-3, NF-3, NEF-3, 8N-3, 12N-3 and 16N-3 are most nearly equivalent to Unified class 3 series UNC-3A/3B, UNF-3A/3B, UNEF-3A/3B, 8UN-3A/3B, 12UN-3A/3B, and 16UN-3A/3B, respectively.