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Then someone made a rod smaller than "0" (zero) that and decided that "-1" or "minus 1" (the next logical (to me, anyway) number on the numerical scale) was bad because someone might not see or understand the dash ("-") before the number and so it was decided to call it a "00" size, (sometimes pronounced as Double-ought or Double Oh or Double Zero... all are the same). Even smaller sizes became "000" and "0000" (Triple Ought and Quadruple Ought).

Others developed sizes based on a descending number sequence where "100" was the smallest (smaller than human hair) and "1" WAS the biggest, and then it got bigger so it became "0" and "00" and "000" etc. (Electrical wire sizes follow this nomenclature.)

Still some others assigned letters to the sizes, "A", "B", "C" etc.

As these various size rods are used as threaded bolts, multiple drill sizes had to be developed to handle a size for a hole to be a through hold without threads (and as things began to need to be more precise then holes needed to be "close fit", "loose fit" and more precise nomenclature, more drill sizes were needed). Also, holes needed to be different sizes based on how thick a thread was to be tapped in a hole, (90% engagement, 70%, 50%, etc.) based on the strength needed vs difficulty in doing the tapping.

All of this created the hodge-podge of drill bit sizes and the need for tables to know which size drill for which size hole for which purpose.

There were "standardizing" committees that sought (and sometimes found) mathematical relationships between the various defacto "standards" and some of the standards were modified slightly to account for slight errors in the mathematical relationships. The defacto "Standard" was "Standardized" on the mathematical value and the original value was slowly eliminated over time as parts already built to the original sizes were replaced/repaired with the new sizes.

If you work with or repair old machinery you will still sometimes run into a bolt size that you have to make yourself if it needs replaced since you cannot get stock or find taps and dies that particular size anymore.