What size is a 39/64" drill bit?

A 39/64" drill bit is 0.6094 in in diameter, which is 15.478 mm. It is the 39/64 in fractional size.

What is the metric equivalent of a 39/64" drill bit?

The closest metric drill to a 39/64" drill bit (15.478 mm) is 15.5 mm, which is 15.500 mm — 0.0009 in larger.

What bolt fits through a 39/64" drill bit hole?

A hole drilled with a 39/64" drill bit is the standard loose clearance hole for 1/2"-28 UNEF, and a clearance hole for 2 other fastener sizes listed on this page.

Fractional drill · 39/64

39/64" Drill Bit Size — Decimal Inch, Millimetre and Tap Sizes

https://shopmath.org/drills/fractional/39-64 · data verified August 1, 2026

A 39/64" drill bit is 0.6094 in (15.478 mm) in diameter. Diameters are nominal.

Series: Fractional
Designation: 39/64
Inch: 0.6094
mm: 15.478
Standard: ANSI/ASME B94.11M

Fractional Drill · 39/64 · nominal diameter

0.6094 in

Millimetre: 15.478mm
Fraction: 39/64in

Nominal diameter. A worn or run-out drill cuts oversize, which leaves less thread in a tapped hole than the table says.

39/64" Drill Bit Size in Inches and Millimetres

The nominal diameter of a 39/64" 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.

39/64" drill bit — decimal inch and millimetre diameter
Property	Value
Diameter, decimal inch	0.6094 in
Diameter, millimetre	15.478 mm
Fraction	39/64 in
Cross-sectional area	0.29165 in²

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

Fasteners That Pass Through a 39/64" Drill Bit Hole

A hole drilled with a 39/64" drill bit is the standard clearance hole for these fasteners — the through-hole the bolt passes freely, not the tapped hole.

Fasteners whose clearance hole is drilled with a 39/64" drill bit
Fastener	Series	Clearance class
1/2"-28 UNEF	Unified Extra Fine (UNEF)	loose
1/2"-20 UNF	Unified Fine (UNF)	loose
1/2"-13 UNC	Unified Coarse (UNC)	loose

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.

39/64" Drill Bit Equivalents in Every Other Drill Series

The closest size to the 39/64" 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 39/64" drill bit
Property	Property	Diameter		Property
Drill	Series	in	mm	Difference, in
#1	Number	0.2280	5.791	−0.3814
Z	Letter	0.4130	10.490	−0.1964
15.5 mm	Metric	0.6102	15.500	+0.0009

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 39/64" 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 39/64" drill bit, by diameter
Property	Property	Diameter
Drill	Series	in	mm
19/32"	Fractional	0.5938	15.081
15.25 mm	Metric	0.6004	15.250
39/64"	Fractional	0.6094	15.478
15.5 mm	Metric	0.6102	15.500
15.75 mm	Metric	0.6201	15.750

Sources and Method for the 39/64" Drill Bit Size

Drill diametercomputed

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

Computed from the standard's formulas, then checked against published tables.

Formula

Fractional drill diameter

Ø  =  39/64 in  =  0.6094 in

Fractional drills are exact fractions of an inch in 1/64 in steps; the decimal is the fraction evaluated, not a measurement.

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 this data is built and checked →

How to Cite This 39/64" Drill Bit Reference

Citation

ShopMath. "39/64" Drill Bit Size — Decimal Inch, Millimetre and Tap Sizes." ShopMath, verified August 1, 2026, https://shopmath.org/drills/fractional/39-64

BibTeX

@misc{shopmath-drills-fractional-39-64,
  title        = {39/64" Drill Bit Size — Decimal Inch, Millimetre and Tap Sizes},
  author       = {{ShopMath}},
  year         = {2026},
  howpublished = {\url{https://shopmath.org/drills/fractional/39-64}},
  note         = {Data verified 2026-08-01}
}

Permanent URL

https://shopmath.org/drills/fractional/39-64

Common Questions About the 39/64" Drill Bit

What size is a 39/64" drill bit?: A 39/64" drill bit is 0.6094 in in diameter, which is 15.478 mm. It is the 39/64 in fractional size.
What is the metric equivalent of a 39/64" drill bit?: The closest metric drill to a 39/64" drill bit (15.478 mm) is 15.5 mm, which is 15.500 mm — 0.0009 in larger.
What bolt fits through a 39/64" drill bit hole?: A hole drilled with a 39/64" drill bit is the standard loose clearance hole for 1/2"-28 UNEF, and a clearance hole for 2 other fastener sizes listed on this page.

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