Contrails ! US drill bit size

Three size systems

Homebuilders are often puzzled by the US drill bit sizes.

The philosophy differs from that of "the rest of the world" : instead of using diameters, there is a gauge system using numbers (number gauge) or letters (letter size).
Add to that a fraction system in 64th of inches (fractional inch).

The three size systems are simultaneously in use for the usual drill bit range.
Mistakes are numerous, and the only solution for the American homebuilder as well as his European counterpart, is the use of a size conversion chart.

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Standard drill bit set

The standard set usually includes 115 pcs : 26 letter bits, 29 fractional-inch bits by 1/64" increments, and bits from 1 through 60.