Letter N drill size
A letter N drill is 0.3020 in (7.671 mm).
- Decimal inch
- 0.3020
- Millimeters
- 7.671
- Nearest 1/64
- 19/64" (+0.0051)
- Type
- letter drill
Nearest equivalents in other systems
| System | Drill | Inch | mm | Difference |
|---|---|---|---|---|
| Fractional | 19/64" | 0.2969 | 7.541 | -0.0051 in |
| Metric | 7.7 mm | 0.3031 | 7.700 | +0.0011 in |
Speeds and feeds: in mild steel an HSS drill starts at about 1,140 RPM and 0.0077 in/rev (8.78 IPM); in 6061 aluminum about 3,160 RPM.
Letter N drill speeds and feeds by material
Jobber-length twist drill, D = 0.3020 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 | 3,160 | 600 | 7,590 | 0.0070 | 22.1 | 53.1 |
| Brass / free-machining | 150 | 1,900 | 400 | 5,060 | 0.0057 | 10.8 | 28.8 |
| Low-carbon steel (1018) | 90 | 1,140 | 300 | 3,790 | 0.0077 | 8.78 | 29.2 |
| Alloy steel (4140, annealed) | 70 | 890 | 250 | 3,160 | 0.0082 | 7.30 | 25.9 |
| Stainless 304 | 40 | 510 | 150 | 1,900 | 0.0051 | 2.60 | 9.69 |
| Gray cast iron | 80 | 1,010 | 250 | 3,160 | 0.0053 | 5.35 | 16.8 |
| Titanium 6Al-4V | 25 | 320 | 100 | 1,260 | 0.0035 | 1.12 | 4.41 |
| Plastics (acetal) | 300 | 3,790 | 500 | 6,320 | 0.0044 | 16.7 | 27.8 |
Metric: Vc (m/min) = SFM × 0.3048; feed (mm/rev) = in/rev × 25.4. In steel, 1,140 RPM × 0.196 mm/rev = 223 mm/min.
Worked example: letter N drill in 1018 steel
- HSS drill in low-carbon steel: 90 SFM.
- RPM = 3.82 × 90 ÷ 0.3020 ≈ 1,140 RPM.
- Feed for a 0.302 in drill in mild steel ≈ 0.0077 in/rev.
- IPM = 1,140 × 0.0077 = 8.78 IPM.
Peck cycle by hole depth
| Depth | Cycle | Peck | Note |
|---|---|---|---|
| 3×D = 0.906 in (23 mm) | G81 (no peck) | None | Up to 3×D a sharp drill clears chips on its own. |
| 5×D = 1.510 in (38.4 mm) | G73 chip-break | 1 × D | Chip-break pecks; full retract if chips pack (soft aluminum, stainless). |
| 8×D = 2.416 in (61.4 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 letter N drill
No standard UNC, UNF or metric tap in our tables calls for a letter N drill. Use it for clearance, pilot or reamer prep holes.
Nearest drills
- 7.7 mm: 0.3031 in / 7.700 mm (+0.0011 in)
- 7.6 mm: 0.2992 in / 7.600 mm (-0.0028 in)
- 7.8 mm: 0.3071 in / 7.800 mm (+0.0051 in)
- 19/64": 0.2969 in / 7.541 mm (-0.0051 in)
Common questions
- What is a letter N drill in decimal and mm?
- 0.3020 in, or 7.671 mm; nearest fractional drill: 19/64" (0.2969 in, -0.0051 in); nearest metric drill: 7.7 mm (0.3031 in, +0.0011 in).
- What RPM for a letter N drill in steel?
- In low-carbon steel (1018) an HSS letter N drill (0.3020 in) runs about 1,140 RPM at 90 SFM; a carbide drill about 3,790 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
- What feed for a letter N drill?
- About 0.0077 in/rev in mild steel, 0.0070 in/rev in aluminum and 0.0051 in/rev in 304 stainless. At 1,140 RPM that is 8.78 IPM in steel (IPM = RPM × IPR).
- What RPM for a letter N drill in aluminum?
- 3,160 RPM with HSS (250 SFM) or up to 7,590 RPM with carbide (600 SFM), feeding about 0.0070 in/rev.
- What size is a letter N drill?
- 0.3020 in / 7.671 mm. The nearest other drills are 7.7 mm (0.3031 in), 7.6 mm (0.2992 in), 7.8 mm (0.3071 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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