letter drill · nominal diameter

R
drill bit size.

A R bit measures 0.3390 in across (8.611 mm).

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

Diameter conversion cross-checked

Calibrated relative diameter · 1 in reference

R · letter

0.3390 in

8.611 mm

DesignationRletter

Inch decimal0.3390nominal

Metric conversion8.611millimetres

Where this size sits from 0 to 1 inch

R · 8.611 mm on a zero to 25.4 millimetre scale. Neighbor marks: 8.6 mm, 8.7 mm.

0 25.4 mm

Show calibrated outline Open in Finder

Measured neighbors

What sits beside R.

“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

8.6 mmmetric 0.3386 inΔ -0.011 mm 8.7 mmmetric 0.3425 inΔ +0.089 mm 8.5 mmmetric 0.3346 inΔ -0.111 mm 11/32fractional 0.3438 inΔ +0.121 mm 8.8 mmmetric 0.3465 inΔ +0.189 mm

Same seriesNEAREST NOMINAL ROWS

Qletter 8.433 mmΔ -0.178 mm Sletter 8.839 mmΔ +0.229 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

Rdrill bit size.

What sits beside R.

ASME.

R
drill bit size.