number drill · nominal diameter

#55
drill bit size.

A #55 bit measures 0.0520 in across (1.321 mm).

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

Diameter conversion cross-checked

Calibrated relative diameter · 1 in reference

#55 · number

0.0520 in

1.321 mm

Designation#55number

Inch decimal0.0520nominal

Metric conversion1.321millimetres

Where this size sits from 0 to 1 inch

#55 · 1.321 mm on a zero to 25.4 millimetre scale. Neighbor marks: 1.3 mm, #54.

0 25.4 mm

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Measured neighbors

What sits beside #55.

“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

1.3 mmmetric 0.0512 inΔ -0.021 mm 1.4 mmmetric 0.0551 inΔ +0.079 mm 1.2 mmmetric 0.0472 inΔ -0.121 mm 3/64fractional 0.0469 inΔ -0.130 mm 1.5 mmmetric 0.0591 inΔ +0.179 mm

Same seriesNEAREST NOMINAL ROWS

#54number 1.397 mmΔ +0.076 mm #56number 1.181 mmΔ -0.140 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

#55drill bit size.

What sits beside #55.

ASME.

#55
drill bit size.