5.5 mm drill size
A 5.5 mm metric drill is 0.2165 in (5.500 mm). It is the cut tap, 50% thread drill for M6x0.75.
- Decimal inch
- 0.2165
- Millimeters
- 5.500
- Nearest 1/64
- 7/32" (-0.0022)
- Type
- metric drill
Nearest equivalents in other systems
Speeds and feeds: in mild steel an HSS drill starts at about 1,590 RPM and 0.0055 in/rev (8.74 IPM); in 6061 aluminum about 4,410 RPM.
5.5 mm drill speeds and feeds by material
Jobber-length twist drill, D = 0.2165 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 | 4,410 | 600 | 10,580 | 0.0052 | 22.9 | 55.0 |
| Brass / free-machining | 150 | 2,650 | 400 | 7,060 | 0.0045 | 11.9 | 31.8 |
| Low-carbon steel (1018) | 90 | 1,590 | 300 | 5,290 | 0.0055 | 8.74 | 29.1 |
| Alloy steel (4140, annealed) | 70 | 1,230 | 250 | 4,410 | 0.0055 | 6.77 | 24.3 |
| Stainless 304 | 40 | 710 | 150 | 2,650 | 0.0036 | 2.56 | 9.54 |
| Gray cast iron | 80 | 1,410 | 250 | 4,410 | 0.0038 | 5.36 | 16.8 |
| Titanium 6Al-4V | 25 | 440 | 100 | 1,760 | 0.0026 | 1.14 | 4.58 |
| Plastics (acetal) | 300 | 5,290 | 500 | 8,820 | 0.0043 | 22.8 | 37.9 |
Metric: Vc (m/min) = SFM × 0.3048; feed (mm/rev) = in/rev × 25.4. In steel, 1,590 RPM × 0.140 mm/rev = 222 mm/min.
Worked example: 5.5 mm drill in 1018 steel
- HSS drill in low-carbon steel: 90 SFM.
- RPM = 3.82 × 90 ÷ 0.2165 ≈ 1,590 RPM.
- Feed for a 0.217 in drill in mild steel ≈ 0.0055 in/rev.
- IPM = 1,590 × 0.0055 = 8.74 IPM.
Peck cycle by hole depth
| Depth | Cycle | Peck | Note |
|---|---|---|---|
| 3×D = 0.650 in (16.5 mm) | G81 (no peck) | None | Up to 3×D a sharp drill clears chips on its own. |
| 5×D = 1.083 in (27.5 mm) | G73 chip-break | 1 × D | Chip-break pecks; full retract if chips pack (soft aluminum, stainless). |
| 8×D = 1.732 in (44 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 5.5 mm drill
- M6x0.75 — cut tap, 50% thread
Nearest drills
- 7/32": 0.2188 in / 5.556 mm (+0.0022 in)
- #3: 0.2130 in / 5.410 mm (-0.0035 in)
- 5.6 mm: 0.2205 in / 5.600 mm (+0.0039 in)
- 5.4 mm: 0.2126 in / 5.400 mm (-0.0039 in)
Common questions
- What is a 5.5 mm drill in decimal and mm?
- 0.2165 in, or 5.500 mm; nearest fractional drill: 7/32" (0.2188 in, +0.0022 in); nearest number / letter drill: #3 (0.2130 in, -0.0035 in).
- What RPM for a 5.5 mm drill in steel?
- In low-carbon steel (1018) an HSS 5.5 mm drill (0.2165 in) runs about 1,590 RPM at 90 SFM; a carbide drill about 5,290 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
- What feed for a 5.5 mm drill?
- About 0.0055 in/rev in mild steel, 0.0052 in/rev in aluminum and 0.0036 in/rev in 304 stainless. At 1,590 RPM that is 8.74 IPM in steel (IPM = RPM × IPR).
- What RPM for a 5.5 mm drill in aluminum?
- 4,410 RPM with HSS (250 SFM) or up to 10,580 RPM with carbide (600 SFM), feeding about 0.0052 in/rev.
- What tap uses a 5.5 mm drill?
- M6x0.75 (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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