number drill · nominal diameter

#19
drill bit size.

A #19 bit measures 0.1660 in across (4.216 mm).

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

Diameter conversion cross-checked

Calibrated relative diameter · 1 in reference

#19 · number

0.1660 in

4.216 mm

Designation#19number

Inch decimal0.1660nominal

Metric conversion4.216millimetres

Where this size sits from 0 to 1 inch

#19 · 4.216 mm on a zero to 25.4 millimetre scale. Neighbor marks: 4.2 mm, 4.3 mm.

0 25.4 mm

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Measured neighbors

What sits beside #19.

“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

4.2 mmmetric 0.1654 inΔ -0.016 mm 4.3 mmmetric 0.1693 inΔ +0.084 mm 4.1 mmmetric 0.1614 inΔ -0.116 mm 11/64fractional 0.1719 inΔ +0.149 mm

Same seriesNEAREST NOMINAL ROWS

#18number 4.305 mmΔ +0.089 mm #20number 4.089 mmΔ -0.127 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

#19drill bit size.

What sits beside #19.

ASME.

#19
drill bit size.