Letter drill · J
J Drill Bit Size — Decimal Inch, Millimetre and Tap Sizes
https://shopmath.org/drills/letter/j · data verified August 1, 2026
A J drill bit is 0.2770 in (7.036 mm) in diameter. The nearest fractional size is 9/32" at 0.2813 in. Diameters are nominal.
- Series
- Letter
- Designation
- J
- Inch
- 0.2770
- mm
- 7.036
- Standard
- ANSI/ASME B94.11M
Letter Drill · J · nominal diameter
0.2770 in
- Millimetre
- 7.036mm
Nominal diameter. A worn or run-out drill cuts oversize, which leaves less thread in a tapped hole than the table says.
J Drill Bit Size in Inches and Millimetres
The nominal diameter of a J 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 | 0.2770 in |
| Diameter, millimetre | 7.036 mm |
| Cross-sectional area | 0.06026 in² |
1 in = 25.4 mm exactly, so the two columns are the same value in different units, not two measurements.
Threads a J Drill Bit Taps
Every thread in this reference whose tap drill is the J drill bit, and the thread engagement it leaves. The engagement asked for and the engagement the drill actually produces are different numbers — that gap is why both columns are here.
| Thread | Series | Thread % asked for | Thread % this drill leaves |
|---|---|---|---|
| 5/16"-32 UNEF | Unified Extra Fine (UNEF) | 85% | 87.4 |
| 5/16"-24 UNF | Unified Fine (UNF) | 65% | 65.6 |
| 5/16"-24 UNF | Unified Fine (UNF) | 70% | 65.6 |
| 5/16"-18 UNC | Unified Coarse (UNC) | 50% | 49.2 |
Values are for cut taps. Rows marked default are the shop-default engagement for that thread.
Fasteners That Pass Through a J Drill Bit Hole
A hole drilled with a J drill bit is the standard clearance hole for these fasteners — the through-hole the bolt passes freely, not the tapped hole.
| Fastener | Series | Clearance class |
|---|---|---|
| 1/4"-32 UNEF | Unified Extra Fine (UNEF) | normal |
| 1/4"-28 UNF | Unified Fine (UNF) | normal |
| 1/4"-20 UNC | Unified Coarse (UNC) | normal |
Clearance classes per ISO 273 (metric) and ASME B18.2.8 (inch): close for located joints, normal for general assembly, loose for slotted or adjustable joints.
J Drill Bit Equivalents in Every Other Drill Series
The closest size to the J 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 | −0.0490 |
| 9/32" | Fractional | 0.2813 | 7.144 | +0.0042 |
| 7 mm | Metric | 0.2756 | 7.000 | −0.0014 |
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 J 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 J 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.
- Tap drill usagecomputed+compiled
bd_warehouse drill_sizes.csv (Apache-2.0) + Wikipedia Drill bit sizes (CC BY-SA 4.0); fractional and metric computed from ANSI B94.11M / BS 328 increment patterns
Verified against drills: 31 checks passed across 1 harness(es)
Part computed from the standard's formulas, part compiled from agreeing public sources.
- 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 J Drill Bit Reference
Citation
ShopMath. "J Drill Bit Size — Decimal Inch, Millimetre and Tap Sizes." ShopMath, verified August 1, 2026, https://shopmath.org/drills/letter/j
BibTeX
@misc{shopmath-drills-letter-j,
title = {J Drill Bit Size — Decimal Inch, Millimetre and Tap Sizes},
author = {{ShopMath}},
year = {2026},
howpublished = {\url{https://shopmath.org/drills/letter/j}},
note = {Data verified 2026-08-01}
}Permanent URL
https://shopmath.org/drills/letter/j
Common Questions About the J Drill Bit
What size is a J drill bit?
- A J drill bit is 0.2770 in in diameter, which is 7.036 mm.
What is the metric equivalent of a J drill bit?
- The closest metric drill to a J drill bit (7.036 mm) is 7 mm, which is 7.000 mm — 0.0014 in smaller.
What fraction is a J drill bit closest to?
- A J drill bit (0.2770 in) sits closest to the 9/32" fractional drill at 0.2813 in, a difference of 0.0042 in.
What bolt fits through a J drill bit hole?
- A hole drilled with a J drill bit is the standard normal clearance hole for 1/4"-32 UNEF, and a clearance hole for 2 other fastener sizes listed on this page.
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