#55 drill size
A #55 number (wire-gauge) drill is 0.0520 in (1.321 mm). It is the cut tap, 50% thread drill for 0-80.
- Decimal inch
- 0.0520
- Millimeters
- 1.321
- Nearest 1/64
- 3/64" (+0.0051)
- Type
- number (wire-gauge) drill
Nearest equivalents in other systems
| System | Drill | Inch | mm | Difference |
|---|---|---|---|---|
| Fractional | 3/64" | 0.0469 | 1.191 | -0.0051 in |
| Metric | 1.3 mm | 0.0512 | 1.300 | -0.0008 in |
Speeds and feeds: in mild steel an HSS drill starts at about 6,610 RPM and 0.0012 in/rev (7.93 IPM); in 6061 aluminum about 18,360 RPM.
#55 drill speeds and feeds by material
Jobber-length twist drill, D = 0.0520 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 | 18,360 | 600 | 44,070 | 0.0012 | 22.0 | 52.9 |
| Brass / free-machining | 150 | 11,020 | 400 | 29,380 | 0.0010 | 11.0 | 29.4 |
| Low-carbon steel (1018) | 90 | 6,610 | 300 | 22,040 | 0.0012 | 7.93 | 26.4 |
| Alloy steel (4140, annealed) | 70 | 5,140 | 250 | 18,360 | 0.0012 | 6.17 | 22.0 |
| Stainless 304 | 40 | 2,940 | 150 | 11,020 | 0.0008 | 2.35 | 8.82 |
| Gray cast iron | 80 | 5,880 | 250 | 18,360 | 0.0007 | 4.12 | 12.8 |
| Titanium 6Al-4V | 25 | 1,840 | 100 | 7,350 | 0.0006 | 1.10 | 4.41 |
| Plastics (acetal) | 300 | 22,040 | 500 | 36,730 | 0.0021 | 46.3 | 77.1 |
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, 6,610 RPM × 0.030 mm/rev = 201 mm/min.
Worked example: #55 drill in 1018 steel
- HSS drill in low-carbon steel: 90 SFM.
- RPM = 3.82 × 90 ÷ 0.0520 ≈ 6,610 RPM.
- Feed for a 0.052 in drill in mild steel ≈ 0.0012 in/rev.
- IPM = 6,610 × 0.0012 = 7.93 IPM.
Peck cycle by hole depth
| Depth | Cycle | Peck | Note |
|---|---|---|---|
| 3×D = 0.156 in (4 mm) | G81 (no peck) | None | Up to 3×D a sharp drill clears chips on its own. |
| 5×D = 0.260 in (6.6 mm) | G73 chip-break | 1 × D | Chip-break pecks; full retract if chips pack (soft aluminum, stainless). |
| 8×D = 0.416 in (10.6 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 #55 drill
- 0-80 — cut tap, 50% thread · tap speeds and feeds
Nearest drills
- 1.3 mm: 0.0512 in / 1.300 mm (-0.0008 in)
- 1.35 mm: 0.0532 in / 1.350 mm (+0.0011 in)
- 1.25 mm: 0.0492 in / 1.250 mm (-0.0028 in)
- #54: 0.0550 in / 1.397 mm (+0.0030 in)
Common questions
- What is a #55 drill in decimal and mm?
- 0.0520 in, or 1.321 mm; nearest fractional drill: 3/64" (0.0469 in, -0.0051 in); nearest metric drill: 1.3 mm (0.0512 in, -0.0008 in).
- What RPM for a #55 drill in steel?
- In low-carbon steel (1018) an HSS #55 drill (0.0520 in) runs about 6,610 RPM at 90 SFM; a carbide drill about 22,040 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
- What feed for a #55 drill?
- About 0.0012 in/rev in mild steel, 0.0012 in/rev in aluminum and 0.0008 in/rev in 304 stainless. At 6,610 RPM that is 7.93 IPM in steel (IPM = RPM × IPR).
- What RPM for a #55 drill in aluminum?
- 18,360 RPM with HSS (250 SFM) or up to 44,070 RPM with carbide (600 SFM), feeding about 0.0012 in/rev.
- What tap uses a #55 drill?
- 0-80 (cut tap, 50% 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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