letter drill · nominal diameter

F
drill bit size.

A F bit measures 0.2570 in across (6.528 mm).

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

Diameter conversion cross-checked

Calibrated relative diameter · 1 in reference

F · letter

0.2570 in

6.528 mm

DesignationFletter

Inch decimal0.2570nominal

Metric conversion6.528millimetres

Where this size sits from 0 to 1 inch

F · 6.528 mm on a zero to 25.4 millimetre scale. Neighbor marks: 6.5 mm, 6.6 mm.

0 25.4 mm

Show calibrated outline Open in Finder

Measured neighbors

What sits beside F.

“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

6.5 mmmetric 0.2559 inΔ -0.028 mm 6.6 mmmetric 0.2598 inΔ +0.072 mm 6.4 mmmetric 0.2520 inΔ -0.128 mm 6.7 mmmetric 0.2638 inΔ +0.172 mm 1/4fractional 0.2500 inΔ -0.178 mm

Same seriesNEAREST NOMINAL ROWS

Gletter 6.629 mmΔ +0.102 mm Eletter 6.350 mmΔ -0.178 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

Fdrill bit size.

What sits beside F.

ASME.

F
drill bit size.