fractional-inch drill · nominal diameter
5/16
drill bit size.
A 5/16 bit measures 0.3125 in across (7.938 mm).
The fractional diameter is exact; decimal and metric values are conversions.
Calibrated relative diameter · 1 in reference
5/16 · fractional
0.3125 in
7.938 mm Designation5/16fractional
Inch decimal0.3125nominal
Metric conversion7.938millimetres
Where this size sits from 0 to 1 inch 5/16 · 7.938 mm on a zero to 25.4 millimetre scale. Neighbor marks: 7.9 mm, 8 mm.
Where this bit is specified
What 5/16 is for.
5/16 is the cutting-tap drill for the thread below— usually the reason this size gets looked up. Engagement is calculated from the basic 60° profile; open a thread for its published row, evidence, and limits.
Measured neighbors
What sits beside 5/16.
“Nearest” means nominal diameter only. It does not make a neighboring size acceptable for a tolerance, tapping, reaming, or fastener application.
This row is at the exposed edge of its series.
Source record
Drill Bit Size Chart.
Fractional sizes are exact rational multiples of one inch.
Open source record