number drill · nominal diameter

#66
drill bit size.

A #66 bit measures 0.0330 in across (0.838 mm).

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

Diameter conversion cross-checked

Calibrated relative diameter · 1 in reference

#66 · number

0.0330 in

0.838 mm

Designation#66number

Inch decimal0.0330nominal

Metric conversion0.838millimetres

Where this size sits from 0 to 1 inch

#66 · 0.838 mm on a zero to 25.4 millimetre scale. Neighbor marks: #67, 0.8 mm.

0 25.4 mm

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Measured neighbors

What sits beside #66.

“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

0.8 mmmetric 0.0315 inΔ -0.038 mm 1/32fractional 0.0313 inΔ -0.044 mm 0.9 mmmetric 0.0354 inΔ +0.062 mm

Same seriesNEAREST NOMINAL ROWS

#67number 0.813 mmΔ -0.025 mm #68number 0.787 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

#66drill bit size.

What sits beside #66.

ASME.

#66
drill bit size.