#50 drill size
A #50 number (wire-gauge) drill is 0.0700 in (1.778 mm). It is the cut tap, 75% thread drill for 2-56.
- Decimal inch
- 0.0700
- Millimeters
- 1.778
- Nearest 1/64
- 1/16" (+0.0075)
- Type
- number (wire-gauge) drill
Nearest equivalents in other systems
Speeds and feeds: in mild steel an HSS drill starts at about 4,910 RPM and 0.0017 in/rev (8.35 IPM); in 6061 aluminum about 13,640 RPM.
#50 drill speeds and feeds by material
Jobber-length twist drill, D = 0.0700 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 | 13,640 | 600 | 32,740 | 0.0016 | 21.8 | 52.4 |
| Brass / free-machining | 150 | 8,190 | 400 | 21,830 | 0.0013 | 10.7 | 28.4 |
| Low-carbon steel (1018) | 90 | 4,910 | 300 | 16,370 | 0.0017 | 8.35 | 27.8 |
| Alloy steel (4140, annealed) | 70 | 3,820 | 250 | 13,640 | 0.0017 | 6.49 | 23.2 |
| Stainless 304 | 40 | 2,180 | 150 | 8,190 | 0.0011 | 2.40 | 9.01 |
| Gray cast iron | 80 | 4,370 | 250 | 13,640 | 0.0010 | 4.37 | 13.6 |
| Titanium 6Al-4V | 25 | 1,360 | 100 | 5,460 | 0.0009 | 1.22 | 4.91 |
| Plastics (acetal) | 300 | 16,370 | 500 | 27,280 | 0.0028 | 45.8 | 76.4 |
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, 4,910 RPM × 0.043 mm/rev = 212 mm/min.
Worked example: #50 drill in 1018 steel
- HSS drill in low-carbon steel: 90 SFM.
- RPM = 3.82 × 90 ÷ 0.0700 ≈ 4,910 RPM.
- Feed for a 0.070 in drill in mild steel ≈ 0.0017 in/rev.
- IPM = 4,910 × 0.0017 = 8.35 IPM.
Peck cycle by hole depth
| Depth | Cycle | Peck | Note |
|---|---|---|---|
| 3×D = 0.210 in (5.3 mm) | G81 (no peck) | None | Up to 3×D a sharp drill clears chips on its own. |
| 5×D = 0.350 in (8.9 mm) | G73 chip-break | 1 × D | Chip-break pecks; full retract if chips pack (soft aluminum, stainless). |
| 8×D = 0.560 in (14.2 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 #50 drill
- 2-56 — cut tap, 75% thread · tap speeds and feeds
- 2-64 — cut tap, 75% thread · tap speeds and feeds
Nearest drills
- 1.8 mm: 0.0709 in / 1.800 mm (+0.0009 in)
- 1.75 mm: 0.0689 in / 1.750 mm (-0.0011 in)
- 1.85 mm: 0.0728 in / 1.850 mm (+0.0028 in)
- #51: 0.0670 in / 1.702 mm (-0.0030 in)
Common questions
- What is a #50 drill in decimal and mm?
- 0.0700 in, or 1.778 mm; nearest fractional drill: 1/16" (0.0625 in, -0.0075 in); nearest metric drill: 1.8 mm (0.0709 in, +0.0009 in).
- What RPM for a #50 drill in steel?
- In low-carbon steel (1018) an HSS #50 drill (0.0700 in) runs about 4,910 RPM at 90 SFM; a carbide drill about 16,370 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
- What feed for a #50 drill?
- About 0.0017 in/rev in mild steel, 0.0016 in/rev in aluminum and 0.0011 in/rev in 304 stainless. At 4,910 RPM that is 8.35 IPM in steel (IPM = RPM × IPR).
- What RPM for a #50 drill in aluminum?
- 13,640 RPM with HSS (250 SFM) or up to 32,740 RPM with carbide (600 SFM), feeding about 0.0016 in/rev.
- What tap uses a #50 drill?
- 2-56 (cut tap, 75% thread); 2-64 (cut tap, 75% 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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