Threads Galvanized bolts and nuts need special thread gages
Thread specifications for galvanized ASTM A325M bolts and A 563M nuts Bolt Nut Thread GO Size Max Pitch Dia Maximum Major Dia GO Size Min Pitch Dia No Go Size Max Pitch Dia Minimum Minor Dia ASTM Allowance M16X2 0 15 083 16 382 15 121 15 333 14 255 0 420 M20X2 5 18 864 20 498 18 906 19 130 17 824 0 530 M22X2 5 20 864 22 488 20 906 21 130