6.4 mm drill size
A 6.4 mm metric drill is 0.2520 in (6.400 mm). It is the cut tap, 50% thread drill for M7x1.
- Decimal inch
- 0.2520
- Millimeters
- 6.400
- Nearest 1/64
- 1/4" (+0.0020)
- Type
- metric drill
Nearest equivalents in other systems
Speeds and feeds: in mild steel an HSS drill starts at about 1,360 RPM and 0.0065 in/rev (8.84 IPM); in 6061 aluminum about 3,790 RPM.
6.4 mm drill speeds and feeds by material
Jobber-length twist drill, D = 0.2520 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 | 3,790 | 600 | 9,100 | 0.0060 | 22.7 | 54.6 |
| Brass / free-machining | 150 | 2,270 | 400 | 6,060 | 0.0053 | 12.0 | 32.1 |
| Low-carbon steel (1018) | 90 | 1,360 | 300 | 4,550 | 0.0065 | 8.84 | 29.6 |
| Alloy steel (4140, annealed) | 70 | 1,060 | 250 | 3,790 | 0.0066 | 7.00 | 25.0 |
| Stainless 304 | 40 | 610 | 150 | 2,270 | 0.0043 | 2.62 | 9.76 |
| Gray cast iron | 80 | 1,210 | 250 | 3,790 | 0.0045 | 5.44 | 17.1 |
| Titanium 6Al-4V | 25 | 380 | 100 | 1,520 | 0.0030 | 1.14 | 4.56 |
| Plastics (acetal) | 300 | 4,550 | 500 | 7,580 | 0.0040 | 18.2 | 30.3 |
Metric: Vc (m/min) = SFM × 0.3048; feed (mm/rev) = in/rev × 25.4. In steel, 1,360 RPM × 0.165 mm/rev = 225 mm/min.
Worked example: 6.4 mm drill in 1018 steel
- HSS drill in low-carbon steel: 90 SFM.
- RPM = 3.82 × 90 ÷ 0.2520 ≈ 1,360 RPM.
- Feed for a 0.252 in drill in mild steel ≈ 0.0065 in/rev.
- IPM = 1,360 × 0.0065 = 8.84 IPM.
Peck cycle by hole depth
| Depth | Cycle | Peck | Note |
|---|---|---|---|
| 3×D = 0.756 in (19.2 mm) | G81 (no peck) | None | Up to 3×D a sharp drill clears chips on its own. |
| 5×D = 1.260 in (32 mm) | G73 chip-break | 1 × D | Chip-break pecks; full retract if chips pack (soft aluminum, stainless). |
| 8×D = 2.016 in (51.2 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 6.4 mm drill
- M7x1 — cut tap, 50% thread · tap speeds and feeds
Nearest drills
- 1/4": 0.2500 in / 6.350 mm (-0.0020 in)
- Letter E: 0.2500 in / 6.350 mm (-0.0020 in)
- 6.3 mm: 0.2480 in / 6.300 mm (-0.0039 in)
- 6.5 mm: 0.2559 in / 6.500 mm (+0.0039 in)
Common questions
- What is a 6.4 mm drill in decimal and mm?
- 0.2520 in, or 6.400 mm; nearest fractional drill: 1/4" (0.2500 in, -0.0020 in); nearest number / letter drill: Letter E (0.2500 in, -0.0020 in).
- What RPM for a 6.4 mm drill in steel?
- In low-carbon steel (1018) an HSS 6.4 mm drill (0.2520 in) runs about 1,360 RPM at 90 SFM; a carbide drill about 4,550 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
- What feed for a 6.4 mm drill?
- About 0.0065 in/rev in mild steel, 0.0060 in/rev in aluminum and 0.0043 in/rev in 304 stainless. At 1,360 RPM that is 8.84 IPM in steel (IPM = RPM × IPR).
- What RPM for a 6.4 mm drill in aluminum?
- 3,790 RPM with HSS (250 SFM) or up to 9,100 RPM with carbide (600 SFM), feeding about 0.0060 in/rev.
- What tap uses a 6.4 mm drill?
- M7x1 (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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