#18 drill size
A #18 number (wire-gauge) drill is 0.1695 in (4.305 mm). It is the cut tap, 50% thread drill for 10-32.
- Decimal inch
- 0.1695
- Millimeters
- 4.305
- Nearest 1/64
- 11/64" (-0.0024)
- Type
- number (wire-gauge) drill
Nearest equivalents in other systems
| System | Drill | Inch | mm | Difference |
|---|---|---|---|---|
| Fractional | 11/64" | 0.1719 | 4.366 | +0.0024 in |
| Metric | 4.3 mm | 0.1693 | 4.300 | -0.0002 in |
Speeds and feeds: in mild steel an HSS drill starts at about 2,030 RPM and 0.0042 in/rev (8.53 IPM); in 6061 aluminum about 5,630 RPM.
#18 drill speeds and feeds by material
Jobber-length twist drill, D = 0.1695 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 | 5,630 | 600 | 13,520 | 0.0040 | 22.5 | 54.1 |
| Brass / free-machining | 150 | 3,380 | 400 | 9,010 | 0.0034 | 11.5 | 30.6 |
| Low-carbon steel (1018) | 90 | 2,030 | 300 | 6,760 | 0.0042 | 8.53 | 28.4 |
| Alloy steel (4140, annealed) | 70 | 1,580 | 250 | 5,630 | 0.0042 | 6.64 | 23.6 |
| Stainless 304 | 40 | 900 | 150 | 3,380 | 0.0028 | 2.52 | 9.46 |
| Gray cast iron | 80 | 1,800 | 250 | 5,630 | 0.0028 | 5.04 | 15.8 |
| Titanium 6Al-4V | 25 | 560 | 100 | 2,250 | 0.0021 | 1.18 | 4.72 |
| Plastics (acetal) | 300 | 6,760 | 500 | 11,270 | 0.0046 | 31.1 | 51.8 |
Metric: Vc (m/min) = SFM × 0.3048; feed (mm/rev) = in/rev × 25.4. In steel, 2,030 RPM × 0.107 mm/rev = 217 mm/min.
Worked example: #18 drill in 1018 steel
- HSS drill in low-carbon steel: 90 SFM.
- RPM = 3.82 × 90 ÷ 0.1695 ≈ 2,030 RPM.
- Feed for a 0.170 in drill in mild steel ≈ 0.0042 in/rev.
- IPM = 2,030 × 0.0042 = 8.53 IPM.
Peck cycle by hole depth
| Depth | Cycle | Peck | Note |
|---|---|---|---|
| 3×D = 0.509 in (12.9 mm) | G81 (no peck) | None | Up to 3×D a sharp drill clears chips on its own. |
| 5×D = 0.848 in (21.5 mm) | G73 chip-break | 1 × D | Chip-break pecks; full retract if chips pack (soft aluminum, stainless). |
| 8×D = 1.356 in (34.4 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 #18 drill
- 10-32 — cut tap, 50% thread · tap speeds and feeds
- 8-32 — Helicoil / STI insert (#8-32×1D) · tap speeds and feeds
Nearest drills
- 4.3 mm: 0.1693 in / 4.300 mm (-0.0002 in)
- 11/64": 0.1719 in / 4.366 mm (+0.0024 in)
- #19: 0.1660 in / 4.216 mm (-0.0035 in)
- #17: 0.1730 in / 4.394 mm (+0.0035 in)
Common questions
- What is a #18 drill in decimal and mm?
- 0.1695 in, or 4.305 mm; nearest fractional drill: 11/64" (0.1719 in, +0.0024 in); nearest metric drill: 4.3 mm (0.1693 in, -0.0002 in).
- What RPM for a #18 drill in steel?
- In low-carbon steel (1018) an HSS #18 drill (0.1695 in) runs about 2,030 RPM at 90 SFM; a carbide drill about 6,760 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
- What feed for a #18 drill?
- About 0.0042 in/rev in mild steel, 0.0040 in/rev in aluminum and 0.0028 in/rev in 304 stainless. At 2,030 RPM that is 8.53 IPM in steel (IPM = RPM × IPR).
- What RPM for a #18 drill in aluminum?
- 5,630 RPM with HSS (250 SFM) or up to 13,520 RPM with carbide (600 SFM), feeding about 0.0040 in/rev.
- What tap uses a #18 drill?
- 10-32 (cut tap, 50% thread); 8-32 (Helicoil / STI insert (#8-32×1D)).
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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