letter drill · nominal diameter
Q
drill bit size.
A Q bit measures 0.3320 in across (8.433 mm).
The inch decimal is the published nominal designation; millimetres are a conversion.
Q · letter
Where this bit is specified
What Q is for.
Q 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 Q.
“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