number drill · nominal diameter

#40
drill bit size.

A #40 bit measures 0.0980 in across (2.489 mm).

The inch decimal is the published nominal designation; millimetres are a conversion.

Diameter conversion cross-checked

Calibrated relative diameter · 1 in reference

#40 · number

0.0980 in

2.489 mm

Designation#40number

Inch decimal0.0980nominal

Metric conversion2.489millimetres

Where this size sits from 0 to 1 inch

#40 · 2.489 mm on a zero to 25.4 millimetre scale. Neighbor marks: 2.5 mm, #39.

0 25.4 mm

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Measured neighbors

What sits beside #40.

“Nearest” means nominal diameter only. It does not make a neighboring size acceptable for a tolerance, tapping, reaming, or fastener application.

Other naming systemsABSOLUTE DIAMETER DELTA

2.5 mmmetric 0.0984 inΔ +0.011 mm 2.4 mmmetric 0.0945 inΔ -0.089 mm 3/32fractional 0.0938 inΔ -0.108 mm 2.6 mmmetric 0.1024 inΔ +0.111 mm

Same seriesNEAREST NOMINAL ROWS

#39number 2.527 mmΔ +0.038 mm #41number 2.438 mmΔ -0.051 mm

Source record

ASME.

The standard text is paywalled. Number and letter series are cross-checked against public manufacturer charts; exact standard edition/page verification remains a release gate.

Open source record

#40drill bit size.

What sits beside #40.

ASME.

#40
drill bit size.