#51 drill size
A #51 number (wire-gauge) drill is 0.0670 in (1.702 mm). It is the form (roll) tap, 65% thread drill for 1-64.
- Decimal inch
- 0.0670
- Millimeters
- 1.702
- Nearest 1/64
- 1/16" (+0.0045)
- Type
- number (wire-gauge) drill
Nearest equivalents in other systems
| System | Drill | Inch | mm | Difference |
|---|---|---|---|---|
| Fractional | 1/16" | 0.0625 | 1.588 | -0.0045 in |
| Metric | 1.7 mm | 0.0669 | 1.700 | -0.0001 in |
Speeds and feeds: in mild steel an HSS drill starts at about 5,130 RPM and 0.0016 in/rev (8.21 IPM); in 6061 aluminum about 14,250 RPM.
#51 drill speeds and feeds by material
Jobber-length twist drill, D = 0.0670 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 | 14,250 | 600 | 34,210 | 0.0015 | 21.4 | 51.3 |
| Brass / free-machining | 150 | 8,550 | 400 | 22,800 | 0.0013 | 11.1 | 29.6 |
| Low-carbon steel (1018) | 90 | 5,130 | 300 | 17,100 | 0.0016 | 8.21 | 27.4 |
| Alloy steel (4140, annealed) | 70 | 3,990 | 250 | 14,250 | 0.0016 | 6.38 | 22.8 |
| Stainless 304 | 40 | 2,280 | 150 | 8,550 | 0.0011 | 2.51 | 9.41 |
| Gray cast iron | 80 | 4,560 | 250 | 14,250 | 0.0010 | 4.56 | 14.3 |
| Titanium 6Al-4V | 25 | 1,430 | 100 | 5,700 | 0.0008 | 1.14 | 4.56 |
| Plastics (acetal) | 300 | 17,100 | 500 | 28,510 | 0.0027 | 46.2 | 77.0 |
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, 5,130 RPM × 0.041 mm/rev = 208 mm/min.
Worked example: #51 drill in 1018 steel
- HSS drill in low-carbon steel: 90 SFM.
- RPM = 3.82 × 90 ÷ 0.0670 ≈ 5,130 RPM.
- Feed for a 0.067 in drill in mild steel ≈ 0.0016 in/rev.
- IPM = 5,130 × 0.0016 = 8.21 IPM.
Peck cycle by hole depth
| Depth | Cycle | Peck | Note |
|---|---|---|---|
| 3×D = 0.201 in (5.1 mm) | G81 (no peck) | None | Up to 3×D a sharp drill clears chips on its own. |
| 5×D = 0.335 in (8.5 mm) | G73 chip-break | 1 × D | Chip-break pecks; full retract if chips pack (soft aluminum, stainless). |
| 8×D = 0.536 in (13.6 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 #51 drill
- 1-64 — form (roll) tap, 65% thread · tap speeds and feeds
- 1-72 — form (roll) tap, 65% thread · tap speeds and feeds
Nearest drills
- 1.7 mm: 0.0669 in / 1.700 mm (-0.0001 in)
- 1.75 mm: 0.0689 in / 1.750 mm (+0.0019 in)
- 1.65 mm: 0.0650 in / 1.650 mm (-0.0020 in)
- #50: 0.0700 in / 1.778 mm (+0.0030 in)
Common questions
- What is a #51 drill in decimal and mm?
- 0.0670 in, or 1.702 mm; nearest fractional drill: 1/16" (0.0625 in, -0.0045 in); nearest metric drill: 1.7 mm (0.0669 in, -0.0001 in).
- What RPM for a #51 drill in steel?
- In low-carbon steel (1018) an HSS #51 drill (0.0670 in) runs about 5,130 RPM at 90 SFM; a carbide drill about 17,100 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
- What feed for a #51 drill?
- About 0.0016 in/rev in mild steel, 0.0015 in/rev in aluminum and 0.0011 in/rev in 304 stainless. At 5,130 RPM that is 8.21 IPM in steel (IPM = RPM × IPR).
- What RPM for a #51 drill in aluminum?
- 14,250 RPM with HSS (250 SFM) or up to 34,210 RPM with carbide (600 SFM), feeding about 0.0015 in/rev.
- What tap uses a #51 drill?
- 1-64 (form (roll) tap, 65% thread); 1-72 (form (roll) tap, 65% thread).
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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