Letter Z drill size
A letter Z drill is 0.4130 in (10.490 mm). It is the form (roll) tap, 65% thread drill for 7/16-20.
- Decimal inch
- 0.4130
- Millimeters
- 10.490
- Nearest 1/64
- 13/32" (+0.0067)
- Type
- letter drill
Nearest equivalents in other systems
Speeds and feeds: in mild steel an HSS drill starts at about 830 RPM and 0.0098 in/rev (8.13 IPM); in 6061 aluminum about 2,310 RPM.
Letter Z drill speeds and feeds by material
Jobber-length twist drill, D = 0.4130 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 | 2,310 | 600 | 5,550 | 0.0090 | 20.8 | 50.0 |
| Brass / free-machining | 150 | 1,390 | 400 | 3,700 | 0.0069 | 9.59 | 25.5 |
| Low-carbon steel (1018) | 90 | 830 | 300 | 2,770 | 0.0098 | 8.13 | 27.1 |
| Alloy steel (4140, annealed) | 70 | 650 | 250 | 2,310 | 0.0108 | 7.02 | 24.9 |
| Stainless 304 | 40 | 370 | 150 | 1,390 | 0.0069 | 2.55 | 9.59 |
| Gray cast iron | 80 | 740 | 250 | 2,310 | 0.0071 | 5.25 | 16.4 |
| Titanium 6Al-4V | 25 | 230 | 100 | 920 | 0.0045 | 1.03 | 4.14 |
| Plastics (acetal) | 300 | 2,770 | 500 | 4,620 | 0.0053 | 14.7 | 24.5 |
Metric: Vc (m/min) = SFM × 0.3048; feed (mm/rev) = in/rev × 25.4. In steel, 830 RPM × 0.249 mm/rev = 207 mm/min.
Worked example: letter Z drill in 1018 steel
- HSS drill in low-carbon steel: 90 SFM.
- RPM = 3.82 × 90 ÷ 0.4130 ≈ 830 RPM.
- Feed for a 0.413 in drill in mild steel ≈ 0.0098 in/rev.
- IPM = 830 × 0.0098 = 8.13 IPM.
Peck cycle by hole depth
| Depth | Cycle | Peck | Note |
|---|---|---|---|
| 3×D = 1.239 in (31.5 mm) | G81 (no peck) | None | Up to 3×D a sharp drill clears chips on its own. |
| 5×D = 2.065 in (52.5 mm) | G73 chip-break | 1 × D | Chip-break pecks; full retract if chips pack (soft aluminum, stainless). |
| 8×D = 3.304 in (83.9 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 Z drill
- 7/16-20 — form (roll) tap, 65% thread · tap speeds and feeds
- 7/16-28 — cut tap, 50% thread
Nearest drills
- 10.5 mm: 0.4134 in / 10.500 mm (+0.0004 in)
- 10.4 mm: 0.4094 in / 10.400 mm (-0.0036 in)
- 10.6 mm: 0.4173 in / 10.600 mm (+0.0043 in)
- 13/32": 0.4063 in / 10.319 mm (-0.0067 in)
Common questions
- What is a letter Z drill in decimal and mm?
- 0.4130 in, or 10.490 mm; nearest fractional drill: 13/32" (0.4063 in, -0.0067 in); nearest metric drill: 10.5 mm (0.4134 in, +0.0004 in).
- What RPM for a letter Z drill in steel?
- In low-carbon steel (1018) an HSS letter Z drill (0.4130 in) runs about 830 RPM at 90 SFM; a carbide drill about 2,770 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
- What feed for a letter Z drill?
- About 0.0098 in/rev in mild steel, 0.0090 in/rev in aluminum and 0.0069 in/rev in 304 stainless. At 830 RPM that is 8.13 IPM in steel (IPM = RPM × IPR).
- What RPM for a letter Z drill in aluminum?
- 2,310 RPM with HSS (250 SFM) or up to 5,550 RPM with carbide (600 SFM), feeding about 0.0090 in/rev.
- What tap uses a letter Z drill?
- 7/16-20 (form (roll) tap, 65% thread); 7/16-28 (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.
Put your skills on a free talent profile
Machines, controls, certs and saved calculations in one profile shops can find.
Create free profileBring shift handoffs to your shop
Stop losing job status between shifts. Every station's notes, counts and issues, handed off cleanly.
See shift handoffs