#39 drill size
A #39 number (wire-gauge) drill is 0.0995 in (2.527 mm).
- Decimal inch
- 0.0995
- Millimeters
- 2.527
- Nearest 1/64
- 3/32" (+0.0058)
- Type
- number (wire-gauge) drill
Nearest equivalents in other systems
| System | Drill | Inch | mm | Difference |
|---|---|---|---|---|
| Fractional | 3/32" | 0.0938 | 2.381 | -0.0057 in |
| Metric | 2.55 mm | 0.1004 | 2.550 | +0.0009 in |
Speeds and feeds: in mild steel an HSS drill starts at about 3,460 RPM and 0.0023 in/rev (7.96 IPM); in 6061 aluminum about 9,600 RPM.
#39 drill speeds and feeds by material
Jobber-length twist drill, D = 0.0995 in. RPM = 3.82 × SFM ÷ D, rounded to 10. Feed per rev scales with diameter and material; IPM = RPM × IPR.
| Material | HSS SFM | HSS RPM | Carbide SFM | Carbide RPM | Feed (in/rev) | HSS IPM | Carbide IPM |
|---|---|---|---|---|---|---|---|
| Aluminum (6061) | 250 | 9,600 | 600 | 23,030 | 0.0023 | 22.1 | 53.0 |
| Brass / free-machining | 150 | 5,760 | 400 | 15,360 | 0.0019 | 10.9 | 29.2 |
| Low-carbon steel (1018) | 90 | 3,460 | 300 | 11,520 | 0.0023 | 7.96 | 26.5 |
| Alloy steel (4140, annealed) | 70 | 2,690 | 250 | 9,600 | 0.0023 | 6.19 | 22.1 |
| Stainless 304 | 40 | 1,540 | 150 | 5,760 | 0.0016 | 2.46 | 9.22 |
| Gray cast iron | 80 | 3,070 | 250 | 9,600 | 0.0014 | 4.30 | 13.4 |
| Titanium 6Al-4V | 25 | 960 | 100 | 3,840 | 0.0012 | 1.15 | 4.61 |
| Plastics (acetal) | 300 | 11,520 | 500 | 19,190 | 0.0040 | 46.1 | 76.8 |
Small drills: the computed RPM is above most spindles. Run at your spindle's maximum and keep the feed per rev; feed drops in proportion.
Metric: Vc (m/min) = SFM × 0.3048; feed (mm/rev) = in/rev × 25.4. In steel, 3,460 RPM × 0.058 mm/rev = 202 mm/min.
Worked example: #39 drill in 1018 steel
- HSS drill in low-carbon steel: 90 SFM.
- RPM = 3.82 × 90 ÷ 0.0995 ≈ 3,460 RPM.
- Feed for a 0.100 in drill in mild steel ≈ 0.0023 in/rev.
- IPM = 3,460 × 0.0023 = 7.96 IPM.
Peck cycle by hole depth
| Depth | Cycle | Peck | Note |
|---|---|---|---|
| 3×D = 0.299 in (7.6 mm) | G81 (no peck) | None | Up to 3×D a sharp drill clears chips on its own. |
| 5×D = 0.498 in (12.6 mm) | G73 chip-break | 1 × D | Chip-break pecks; full retract if chips pack (soft aluminum, stainless). |
| 8×D = 0.796 in (20.2 mm) | G83 full retract | 0.5-1 × D, shrinking with depth | Retract to clear chips; reduce feed ~10-20% past 5×D. |
Taps that use a #39 drill
No standard UNC, UNF or metric tap in our tables calls for a #39 drill. Use it for clearance, pilot or reamer prep holes.
Nearest drills
- 2.55 mm: 0.1004 in / 2.550 mm (+0.0009 in)
- 2.5 mm: 0.0984 in / 2.500 mm (-0.0011 in)
- #40: 0.0980 in / 2.489 mm (-0.0015 in)
- #38: 0.1015 in / 2.578 mm (+0.0020 in)
Common questions
- What is a #39 drill in decimal and mm?
- 0.0995 in, or 2.527 mm; nearest fractional drill: 3/32" (0.0938 in, -0.0057 in); nearest metric drill: 2.55 mm (0.1004 in, +0.0009 in).
- What RPM for a #39 drill in steel?
- In low-carbon steel (1018) an HSS #39 drill (0.0995 in) runs about 3,460 RPM at 90 SFM; a carbide drill about 11,520 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
- What feed for a #39 drill?
- About 0.0023 in/rev in mild steel, 0.0023 in/rev in aluminum and 0.0016 in/rev in 304 stainless. At 3,460 RPM that is 7.96 IPM in steel (IPM = RPM × IPR).
- What RPM for a #39 drill in aluminum?
- 9,600 RPM with HSS (250 SFM) or up to 23,030 RPM with carbide (600 SFM), feeding about 0.0023 in/rev.
- What size is a #39 drill?
- 0.0995 in / 2.527 mm. The nearest other drills are 2.55 mm (0.1004 in), 2.5 mm (0.0984 in), #40 (0.0980 in).
Nearby drill sizes
Sources
- Machinery's Handbook, 31st ed., Speeds and Feeds for Drilling, Reaming and Threading (Tables 17-23) — HSS and carbide drilling SFM (rounded).
- RedLine Tools (Productivity Inc.) catalog p. 340, Cobalt & HSS Drills Speeds & Feeds — feed per rev by drill diameter and material (middle of the catalog range).
- ASME B94.11M twist drills: number (#1-#80) and letter (A-Z) drill sizes; drill size reference.
Material feed multipliers (aluminum 1.3×, brass 1.1×, 4140 0.85×, stainless and titanium 0.7× the mild-steel feed) are JobLine estimates. Peck guidance is JobLine shop practice. Use your drill maker's data first.
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