8.5 mm drill size
A 8.5 mm metric drill is 0.3347 in (8.500 mm). It is the cut tap, 75% thread drill for M10×1.5.
- Decimal inch
- 0.3347
- Millimeters
- 8.500
- Nearest 1/64
- 21/64" (+0.0065)
- Type
- metric drill
Nearest equivalents in other systems
Speeds and feeds: in mild steel an HSS drill starts at about 1,030 RPM and 0.0085 in/rev (8.76 IPM); in 6061 aluminum about 2,850 RPM.
8.5 mm drill speeds and feeds by material
Jobber-length twist drill, D = 0.3347 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 | 2,850 | 600 | 6,850 | 0.0077 | 21.9 | 52.8 |
| Brass / free-machining | 150 | 1,710 | 400 | 4,570 | 0.0059 | 10.1 | 27.0 |
| Low-carbon steel (1018) | 90 | 1,030 | 300 | 3,420 | 0.0085 | 8.76 | 29.1 |
| Alloy steel (4140, annealed) | 70 | 800 | 250 | 2,850 | 0.0092 | 7.36 | 26.2 |
| Stainless 304 | 40 | 460 | 150 | 1,710 | 0.0056 | 2.58 | 9.58 |
| Gray cast iron | 80 | 910 | 250 | 2,850 | 0.0059 | 5.37 | 16.8 |
| Titanium 6Al-4V | 25 | 290 | 100 | 1,140 | 0.0038 | 1.10 | 4.33 |
| Plastics (acetal) | 300 | 3,420 | 500 | 5,710 | 0.0047 | 16.1 | 26.8 |
Metric: Vc (m/min) = SFM × 0.3048; feed (mm/rev) = in/rev × 25.4. In steel, 1,030 RPM × 0.216 mm/rev = 222 mm/min.
Worked example: 8.5 mm drill in 1018 steel
- HSS drill in low-carbon steel: 90 SFM.
- RPM = 3.82 × 90 ÷ 0.3347 ≈ 1,030 RPM.
- Feed for a 0.335 in drill in mild steel ≈ 0.0085 in/rev.
- IPM = 1,030 × 0.0085 = 8.76 IPM.
Peck cycle by hole depth
| Depth | Cycle | Peck | Note |
|---|---|---|---|
| 3×D = 1.004 in (25.5 mm) | G81 (no peck) | None | Up to 3×D a sharp drill clears chips on its own. |
| 5×D = 1.673 in (42.5 mm) | G73 chip-break | 1 × D | Chip-break pecks; full retract if chips pack (soft aluminum, stainless). |
| 8×D = 2.677 in (68 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 8.5 mm drill
- M10×1.5 — cut tap, 75% thread · tap speeds and feeds
Nearest drills
- Letter Q: 0.3320 in / 8.433 mm (-0.0027 in)
- 8.6 mm: 0.3386 in / 8.600 mm (+0.0039 in)
- 8.4 mm: 0.3307 in / 8.400 mm (-0.0039 in)
- Letter R: 0.3390 in / 8.611 mm (+0.0043 in)
Common questions
- What is a 8.5 mm drill in decimal and mm?
- 0.3347 in, or 8.500 mm; nearest fractional drill: 21/64" (0.3281 in, -0.0065 in); nearest number / letter drill: Letter Q (0.3320 in, -0.0027 in).
- What RPM for a 8.5 mm drill in steel?
- In low-carbon steel (1018) an HSS 8.5 mm drill (0.3347 in) runs about 1,030 RPM at 90 SFM; a carbide drill about 3,420 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
- What feed for a 8.5 mm drill?
- About 0.0085 in/rev in mild steel, 0.0077 in/rev in aluminum and 0.0056 in/rev in 304 stainless. At 1,030 RPM that is 8.76 IPM in steel (IPM = RPM × IPR).
- What RPM for a 8.5 mm drill in aluminum?
- 2,850 RPM with HSS (250 SFM) or up to 6,850 RPM with carbide (600 SFM), feeding about 0.0077 in/rev.
- What tap uses a 8.5 mm drill?
- M10×1.5 (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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