Other naming systemsABSOLUTE DIAMETER DELTA
fractional-inch drill · nominal diameter
1
drill bit size.
A 1 bit measures 1.0000 in across (25.400 mm).
The fractional diameter is exact; decimal and metric values are conversions.
Calibrated relative diameter · 1 in reference
1 · fractional
1.0000 in
25.400 mm Designation1fractional
Inch decimal1.0000nominal
Metric conversion25.400millimetres
Where this size sits from 0 to 1 inch 1 · 25.400 mm on a zero to 25.4 millimetre scale. Neighbor marks: 63/64, 31/32.
Measured neighbors
What sits beside 1.
“Nearest” means nominal diameter only. It does not make a neighboring size acceptable for a tolerance, tapping, reaming, or fastener application.
Source record
Drill Bit Size Chart.
Fractional sizes are exact rational multiples of one inch.
Open source record