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.
F · letter
Where this bit is specified
What F is for.
F 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 F.
“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