What size is a #42 drill bit?

A #42 drill bit is 0.0935 in in diameter, which is 2.375 mm.

What thread does a #42 drill bit tap?

A #42 drill bit is the tap drill for #4-48 UNF at 75% requested thread engagement, where it leaves 68.4% thread with a cut tap.

What is the metric equivalent of a #42 drill bit?

The closest metric drill to a #42 drill bit (2.375 mm) is 2.35 mm, which is 2.350 mm — 0.0010 in smaller.

What fraction is a #42 drill bit closest to?

A #42 drill bit (0.0935 in) sits closest to the 3/32" fractional drill at 0.0938 in, a difference of 0.0003 in.

Number drill · #42

#42 Drill Bit Size — Decimal Inch, Millimetre and Tap Sizes

https://shopmath.org/drills/number/42 · data verified August 1, 2026

A #42 drill bit is 0.0935 in (2.375 mm) in diameter. It is the tap drill for #4-48 UNF at 75% thread engagement with a cut tap, where it leaves 68.4% thread. The nearest fractional size is 3/32" at 0.0938 in. Diameters are nominal.

Series: Number
Designation: #42
Inch: 0.0935
mm: 2.375
Standard: ANSI/ASME B94.11M

Number Drill · #42 · nominal diameter

0.0935 in

Millimetre: 2.375mm
Taps: #4-48 UNF

Nominal diameter. As a tap drill it leaves 68.4% thread in #4-48 UNF with a cut tap.

#42 Drill Bit Size in Inches and Millimetres

The nominal diameter of a #42 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.

#42 drill bit — decimal inch and millimetre diameter
Property	Value
Diameter, decimal inch	0.0935 in
Diameter, millimetre	2.375 mm
Cross-sectional area	0.00687 in²

1 in = 25.4 mm exactly, so the two columns are the same value in different units, not two measurements.

Threads a #42 Drill Bit Taps

Every thread in this reference whose tap drill is the #42 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.

Threads tapped with a #42 drill bit, by thread engagement
Thread	Series	Thread % asked for	Thread % this drill leaves
#4-48 UNF	Unified Fine (UNF)	75%default	68.4
#4-48 UNF	Unified Fine (UNF)	70%	68.4
#4-40 UNC	Unified Coarse (UNC)	60%	57.0

Values are for cut taps. Rows marked default are the shop-default engagement for that thread.

#42 Drill Bit Equivalents in Every Other Drill Series

The closest size to the #42 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.

Nearest number, letter, fractional and metric equivalents to a #42 drill bit
Property	Property	Diameter		Property
Drill	Series	in	mm	Difference, in
A	Letter	0.2340	5.944	+0.1405
3/32"	Fractional	0.0938	2.381	+0.0003
2.35 mm	Metric	0.0925	2.350	−0.0010

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 #42 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.

Standard drill sizes adjacent to a #42 drill bit, by diameter
Property	Property	Diameter
Drill	Series	in	mm
2.3 mm	Metric	0.0906	2.300
2.35 mm	Metric	0.0925	2.350
#42	Number	0.0935	2.375
3/32"	Fractional	0.0938	2.381
2.4 mm	Metric	0.0945	2.400

Sources and Method for the #42 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.
Tap drill usage assumes cut taps. #4-48 UNF at 75% requested engagement is what this drill is normally bought for.
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 this data is built and checked →

How to Cite This #42 Drill Bit Reference

Citation

ShopMath. "#42 Drill Bit Size — Decimal Inch, Millimetre and Tap Sizes." ShopMath, verified August 1, 2026, https://shopmath.org/drills/number/42

BibTeX

@misc{shopmath-drills-number-42,
  title        = {#42 Drill Bit Size — Decimal Inch, Millimetre and Tap Sizes},
  author       = {{ShopMath}},
  year         = {2026},
  howpublished = {\url{https://shopmath.org/drills/number/42}},
  note         = {Data verified 2026-08-01}
}

Permanent URL

https://shopmath.org/drills/number/42

Common Questions About the #42 Drill Bit

What size is a #42 drill bit?: A #42 drill bit is 0.0935 in in diameter, which is 2.375 mm.
What thread does a #42 drill bit tap?: A #42 drill bit is the tap drill for #4-48 UNF at 75% requested thread engagement, where it leaves 68.4% thread with a cut tap.
What is the metric equivalent of a #42 drill bit?: The closest metric drill to a #42 drill bit (2.375 mm) is 2.35 mm, which is 2.350 mm — 0.0010 in smaller.
What fraction is a #42 drill bit closest to?: A #42 drill bit (0.0935 in) sits closest to the 3/32" fractional drill at 0.0938 in, a difference of 0.0003 in.

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