What is a #38 drill in decimal and mm?

0.1015 in, or 2.578 mm; nearest fractional drill: 3/32" (0.0938 in, -0.0077 in); nearest metric drill: 2.6 mm (0.1024 in, +0.0009 in).

What RPM for a #38 drill in steel?

In low-carbon steel (1018) an HSS #38 drill (0.1015 in) runs about 3,390 RPM at 90 SFM; a carbide drill about 11,290 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.

What feed for a #38 drill?

About 0.0024 in/rev in mild steel, 0.0023 in/rev in aluminum and 0.0016 in/rev in 304 stainless. At 3,390 RPM that is 8.14 IPM in steel (IPM = RPM × IPR).

What RPM for a #38 drill in aluminum?

9,410 RPM with HSS (250 SFM) or up to 22,580 RPM with carbide (600 SFM), feeding about 0.0023 in/rev.

What tap uses a #38 drill?

5-40 (cut tap, 75% thread); 4-40 (form (roll) tap, 65% thread).

#38 drill size

A #38 number (wire-gauge) drill is 0.1015 in (2.578 mm). It is the cut tap, 75% thread drill for 5-40.

Decimal inch: 0.1015
Millimeters: 2.578
Nearest 1/64: 3/32" (+0.0078)
Type: number (wire-gauge) drill

Nearest equivalents in other systems

Drills closest to #38
System	Drill	Inch	mm	Difference
Fractional	3/32"	0.0938	2.381	-0.0077 in
Metric	2.6 mm	0.1024	2.600	+0.0009 in

Speeds and feeds: in mild steel an HSS drill starts at about 3,390 RPM and 0.0024 in/rev (8.14 IPM); in 6061 aluminum about 9,410 RPM.

#38 drill speeds and feeds by material

Jobber-length twist drill, D = 0.1015 in. RPM = 3.82 × SFM ÷ D, rounded to 10. Feed per rev scales with diameter and material; IPM = RPM × IPR.

#38 drilling speeds
Material	HSS SFM	HSS RPM	Carbide SFM	Carbide RPM	Feed (in/rev)	HSS IPM	Carbide IPM
Aluminum (6061)	250	9,410	600	22,580	0.0023	21.6	51.9
Brass / free-machining	150	5,640	400	15,050	0.0019	10.7	28.6
Low-carbon steel (1018)	90	3,390	300	11,290	0.0024	8.14	27.1
Alloy steel (4140, annealed)	70	2,630	250	9,410	0.0024	6.31	22.6
Stainless 304	40	1,510	150	5,640	0.0016	2.42	9.02
Gray cast iron	80	3,010	250	9,410	0.0015	4.51	14.1
Titanium 6Al-4V	25	940	100	3,760	0.0013	1.22	4.89
Plastics (acetal)	300	11,290	500	18,820	0.0041	46.3	77.2

Small drills: the computed RPM is above most spindles. Run at your spindle's maximum and keep the feed per rev; feed drops in proportion.

Metric: Vc (m/min) = SFM × 0.3048; feed (mm/rev) = in/rev × 25.4. In steel, 3,390 RPM × 0.061 mm/rev = 207 mm/min.

Worked example: #38 drill in 1018 steel

HSS drill in low-carbon steel: 90 SFM.
RPM = 3.82 × 90 ÷ 0.1015 ≈ 3,390 RPM.
Feed for a 0.102 in drill in mild steel ≈ 0.0024 in/rev.
IPM = 3,390 × 0.0024 = 8.14 IPM.

Peck cycle by hole depth

#38 drill: depth and canned cycle
Depth	Cycle	Peck	Note
3×D = 0.305 in (7.7 mm)	G81 (no peck)	None	Up to 3×D a sharp drill clears chips on its own.
5×D = 0.508 in (12.9 mm)	G73 chip-break	1 × D	Chip-break pecks; full retract if chips pack (soft aluminum, stainless).
8×D = 0.812 in (20.6 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 #38 drill

5-40 — cut tap, 75% thread · tap speeds and feeds
4-40 — form (roll) tap, 65% thread · tap speeds and feeds

Nearest drills

2.6 mm: 0.1024 in / 2.600 mm (+0.0009 in)
2.55 mm: 0.1004 in / 2.550 mm (-0.0011 in)
#39: 0.0995 in / 2.527 mm (-0.0020 in)
#37: 0.1040 in / 2.642 mm (+0.0025 in)

Drill speed calculator, prefilled for #38 Drill finder: sizes near #38 Number drill chart Decimal equivalent chart

Common questions

What is a #38 drill in decimal and mm?: 0.1015 in, or 2.578 mm; nearest fractional drill: 3/32" (0.0938 in, -0.0077 in); nearest metric drill: 2.6 mm (0.1024 in, +0.0009 in).
What RPM for a #38 drill in steel?: In low-carbon steel (1018) an HSS #38 drill (0.1015 in) runs about 3,390 RPM at 90 SFM; a carbide drill about 11,290 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
What feed for a #38 drill?: About 0.0024 in/rev in mild steel, 0.0023 in/rev in aluminum and 0.0016 in/rev in 304 stainless. At 3,390 RPM that is 8.14 IPM in steel (IPM = RPM × IPR).
What RPM for a #38 drill in aluminum?: 9,410 RPM with HSS (250 SFM) or up to 22,580 RPM with carbide (600 SFM), feeding about 0.0023 in/rev.
What tap uses a #38 drill?: 5-40 (cut tap, 75% thread); 4-40 (form (roll) tap, 65% 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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