Drill Bit Size Chart
Tools
Data 2026.07.13-audit.1
Checking connection

letter drill · nominal diameter

U
drill bit size.

A U bit measures 0.3680 in across (9.347 mm).

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

Diameter conversion cross-checked
Calibrated relative diameter · 1 in reference

U · letter

0.3680 in
9.347 mm
DesignationUletter
Inch decimal0.3680nominal
Metric conversion9.347millimetres
Where this size sits from 0 to 1 inch
U · 9.347 mm on a zero to 25.4 millimetre scale. Neighbor marks: 9.3 mm, 9.4 mm.
0 25.4 mm
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Where this bit is specified

What U is for.

U is the cutting-tap drill for the thread below— usually the reason this size gets looked up. Engagement is calculated from the basic 60° profile; open a thread for its published row, evidence, and limits.

Measured neighbors

What sits beside U.

“Nearest” means nominal diameter only. It does not make a neighboring size acceptable for a tolerance, tapping, reaming, or fastener application.

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