#81 drill size
A #81 number (wire-gauge) drill is 0.0130 in (0.330 mm).
- Decimal inch
- 0.0130
- Millimeters
- 0.330
- Nearest 1/64
- 1/64" (-0.0026)
- Type
- number (wire-gauge) drill
Nearest equivalents in other systems
| System | Drill | Inch | mm | Difference |
|---|---|---|---|---|
| Fractional | 1/64" | 0.0156 | 0.397 | +0.0026 in |
| Metric | 0.35 mm | 0.0138 | 0.350 | +0.0008 in |
Speeds and feeds: in mild steel an HSS drill starts at about 26,440 RPM and 0.0007 in/rev (18.5 IPM); in 6061 aluminum about 73,460 RPM.
#81 drill speeds and feeds by material
Jobber-length twist drill, D = 0.0130 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 | 73,460 | 600 | 176,290 | 0.0007 | 51.4 | 123.4 |
| Brass / free-machining | 150 | 44,070 | 400 | 117,530 | 0.0006 | 26.4 | 70.5 |
| Low-carbon steel (1018) | 90 | 26,440 | 300 | 88,150 | 0.0007 | 18.5 | 61.7 |
| Alloy steel (4140, annealed) | 70 | 20,570 | 250 | 73,460 | 0.0007 | 14.4 | 51.4 |
| Stainless 304 | 40 | 11,750 | 150 | 44,070 | 0.0005 | 5.88 | 22.0 |
| Gray cast iron | 80 | 23,510 | 250 | 73,460 | 0.0005 | 11.8 | 36.7 |
| Titanium 6Al-4V | 25 | 7,350 | 100 | 29,380 | 0.0004 | 2.94 | 11.8 |
| Plastics (acetal) | 300 | 88,150 | 500 | 146,910 | 0.0013 | 114.6 | 191.0 |
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, 26,440 RPM × 0.018 mm/rev = 470 mm/min.
Worked example: #81 drill in 1018 steel
- HSS drill in low-carbon steel: 90 SFM.
- RPM = 3.82 × 90 ÷ 0.0130 ≈ 26,440 RPM.
- Feed for a 0.013 in drill in mild steel ≈ 0.0007 in/rev.
- IPM = 26,440 × 0.0007 = 18.5 IPM.
Peck cycle by hole depth
| Depth | Cycle | Peck | Note |
|---|---|---|---|
| 3×D = 0.039 in (1 mm) | G81 (no peck) | None | Up to 3×D a sharp drill clears chips on its own. |
| 5×D = 0.065 in (1.7 mm) | G73 chip-break | 1 × D | Chip-break pecks; full retract if chips pack (soft aluminum, stainless). |
| 8×D = 0.104 in (2.6 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 #81 drill
No standard UNC, UNF or metric tap in our tables calls for a #81 drill. Use it for clearance, pilot or reamer prep holes.
Nearest drills
- #82: 0.0125 in / 0.318 mm (-0.0005 in)
- #80: 0.0135 in / 0.343 mm (+0.0005 in)
- 0.35 mm: 0.0138 in / 0.350 mm (+0.0008 in)
- #83: 0.0120 in / 0.305 mm (-0.0010 in)
Common questions
- What is a #81 drill in decimal and mm?
- 0.0130 in, or 0.330 mm; nearest fractional drill: 1/64" (0.0156 in, +0.0026 in); nearest metric drill: 0.35 mm (0.0138 in, +0.0008 in).
- What RPM for a #81 drill in steel?
- In low-carbon steel (1018) an HSS #81 drill (0.0130 in) runs about 26,440 RPM at 90 SFM; a carbide drill about 88,150 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
- What feed for a #81 drill?
- About 0.0007 in/rev in mild steel, 0.0007 in/rev in aluminum and 0.0005 in/rev in 304 stainless. At 26,440 RPM that is 18.5 IPM in steel (IPM = RPM × IPR).
- What RPM for a #81 drill in aluminum?
- 73,460 RPM with HSS (250 SFM) or up to 176,290 RPM with carbide (600 SFM), feeding about 0.0007 in/rev.
- What size is a #81 drill?
- 0.0130 in / 0.330 mm. The nearest other drills are #82 (0.0125 in), #80 (0.0135 in), 0.35 mm (0.0138 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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