Letter drill · B
B Drill Bit Size — Decimal Inch, Millimetre and Tap Sizes
https://shopmath.org/drills/letter/b · data verified August 1, 2026
A B drill bit is 0.2380 in (6.045 mm) in diameter. The nearest fractional size is 15/64" at 0.2344 in. Diameters are nominal.
- Series
- Letter
- Designation
- B
- Inch
- 0.2380
- mm
- 6.045
- Standard
- ANSI/ASME B94.11M
Letter Drill · B · nominal diameter
0.2380 in
- Millimetre
- 6.045mm
Nominal diameter. A worn or run-out drill cuts oversize, which leaves less thread in a tapped hole than the table says.
B Drill Bit Size in Inches and Millimetres
The nominal diameter of a B drill bit. Drill sizes are nominal — a worn drill, run-out or a soft material that closes in behind the cut all move the finished hole.
| Property | Value |
|---|---|
| Diameter, decimal inch | 0.2380 in |
| Diameter, millimetre | 6.045 mm |
| Cross-sectional area | 0.04449 in² |
1 in = 25.4 mm exactly, so the two columns are the same value in different units, not two measurements.
B Drill Bit Equivalents in Every Other Drill Series
The closest size to the B drill bit in each of the other three indexes, with the difference in inches. None of them is the same drill — check the difference before substituting one into a tapped hole.
| Property | Property | Diameter | Property | |
|---|---|---|---|---|
| Drill | Series | in | mm | Difference, in |
| #1 | Number | 0.2280 | 5.791 | −0.0100 |
| 15/64" | Fractional | 0.2344 | 5.953 | −0.0036 |
| 6 mm | Metric | 0.2362 | 6.000 | −0.0018 |
A positive difference means the equivalent drill is larger, which leaves less thread in a tapped hole. Sizes without a link are stored for the nearest-drill calculation but do not carry their own page.
Drill Sizes Either Side of the B Drill Bit
Ordered by diameter across all four indexes, so the next size up may be a letter, a fraction or a metric drill rather than the next one in this series.
Sources and Method for the B Drill Bit Size
- Drill diametercompiled
Number/letter: bd_warehouse drill_sizes.csv (Apache-2.0) cross-checked against Wikipedia Drill bit sizes (CC BY-SA 4.0). Fractional: computed 1/64 in steps per ANSI B94.11M. Metric: computed BS 328 increment pattern.
Verified against Wikipedia Drill bit sizes (CC BY-SA 4.0); 31/31 checks passed
Compiled from independent public sources that agree cell-for-cell.
- Assumptions
- Diameters are nominal. Drill manufacturing tolerance, wear and run-out all cut oversize, and every one of those moves a tapped hole toward less thread than the table says.
- Dataset scope: Number sizes #61-#80 are stored but tagged demandTier 'extended' — query-space-map.md Appendix A found the tail thinning in the 60s. Sizes below #80 and metric sizes above 25.0 mm excluded.
- Data last verified
- August 1, 2026
How to Cite This B Drill Bit Reference
Citation
ShopMath. "B Drill Bit Size — Decimal Inch, Millimetre and Tap Sizes." ShopMath, verified August 1, 2026, https://shopmath.org/drills/letter/b
BibTeX
@misc{shopmath-drills-letter-b,
title = {B Drill Bit Size — Decimal Inch, Millimetre and Tap Sizes},
author = {{ShopMath}},
year = {2026},
howpublished = {\url{https://shopmath.org/drills/letter/b}},
note = {Data verified 2026-08-01}
}Permanent URL
https://shopmath.org/drills/letter/b
Common Questions About the B Drill Bit
What size is a B drill bit?
- A B drill bit is 0.2380 in in diameter, which is 6.045 mm.
What is the metric equivalent of a B drill bit?
- The closest metric drill to a B drill bit (6.045 mm) is 6 mm, which is 6.000 mm — 0.0018 in smaller.
What fraction is a B drill bit closest to?
- A B drill bit (0.2380 in) sits closest to the 15/64" fractional drill at 0.2344 in, a difference of 0.0036 in.
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