I recently purchased an old 13 piece set of IRWIN Solid Centre Stem Auger Bits from a used tools store for use in a hand-brace. The bits came in a wooden box with a swing-out lower drawer, and a black descriptive label on the inside lid. The box label says "1 set 20 1-2 quarters". What do these numbers mean? The bit numbers are 4, 5, 6, 7, 8, 10, 12, 14, and 16.
The 4, 5, 6 etc refers to the size in sixteenths. 4 is 4/16 or 1/4". 6 is 6/16 or 3/8". 20-1/2 quarters refers to the total size of the set. This is the way they did it in the old days.