Jobber Drills - Gauge Sizes

Gauge size drill calculations are generally made utilising a reference book or table. Number drill bit gauge sizes are analogous to but different from American wire gauge. Number gauge is most commonly used from size 80 (the smallest) to size 1 (the largest) followed by letter
gauge size A (the smallest) to size Z (the largest). The number gauge actually runs to No. 97, but sizes smaller than No. 80 are very rarely used.