number drill · nominal diameter

#18
drill bit size.

A #18 bit measures 0.1695 in across (4.305 mm).

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

Diameter conversion cross-checked

Calibrated relative diameter · 1 in reference

#18 · number

0.1695 in

4.305 mm

Designation#18number

Inch decimal0.1695nominal

Metric conversion4.305millimetres

Where this size sits from 0 to 1 inch

#18 · 4.305 mm on a zero to 25.4 millimetre scale. Neighbor marks: 4.3 mm, 11/64.

0 25.4 mm

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Measured neighbors

What sits beside #18.

“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

4.3 mmmetric 0.1693 inΔ -0.005 mm 11/64fractional 0.1719 inΔ +0.060 mm 4.4 mmmetric 0.1732 inΔ +0.095 mm 4.2 mmmetric 0.1654 inΔ -0.105 mm 4.5 mmmetric 0.1772 inΔ +0.195 mm

Same seriesNEAREST NOMINAL ROWS

#19number 4.216 mmΔ -0.089 mm #17number 4.394 mmΔ +0.089 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

#18drill bit size.

What sits beside #18.

ASME.

#18
drill bit size.