What is a #40 drill in decimal and mm?

0.0980 in, or 2.489 mm; nearest fractional drill: 3/32" (0.0938 in, -0.0043 in); nearest metric drill: 2.5 mm (0.0984 in, +0.0004 in).

What RPM for a #40 drill in steel?

In low-carbon steel (1018) an HSS #40 drill (0.0980 in) runs about 3,510 RPM at 90 SFM; a carbide drill about 11,690 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.

What feed for a #40 drill?

About 0.0023 in/rev in mild steel, 0.0022 in/rev in aluminum and 0.0016 in/rev in 304 stainless. At 3,510 RPM that is 8.07 IPM in steel (IPM = RPM × IPR).

What RPM for a #40 drill in aluminum?

9,740 RPM with HSS (250 SFM) or up to 23,390 RPM with carbide (600 SFM), feeding about 0.0022 in/rev.

#40 drill size

A #40 number (wire-gauge) drill is 0.0980 in (2.489 mm). It is the cut tap, 50% thread drill for 4-48.

Decimal inch: 0.0980
Millimeters: 2.489
Nearest 1/64: 3/32" (+0.0043)
Type: number (wire-gauge) drill

Nearest equivalents in other systems

Drills closest to #40
System	Drill	Inch	mm	Difference
Fractional	3/32"	0.0938	2.381	-0.0043 in
Metric	2.5 mm	0.0984	2.500	+0.0004 in

Speeds and feeds: in mild steel an HSS drill starts at about 3,510 RPM and 0.0023 in/rev (8.07 IPM); in 6061 aluminum about 9,740 RPM.

#40 drill speeds and feeds by material

Jobber-length twist drill, D = 0.0980 in. RPM = 3.82 × SFM ÷ D, rounded to 10. Feed per rev scales with diameter and material; IPM = RPM × IPR.

#40 drilling speeds
Material	HSS SFM	HSS RPM	Carbide SFM	Carbide RPM	Feed (in/rev)	HSS IPM	Carbide IPM
Aluminum (6061)	250	9,740	600	23,390	0.0022	21.4	51.5
Brass / free-machining	150	5,850	400	15,590	0.0019	11.1	29.6
Low-carbon steel (1018)	90	3,510	300	11,690	0.0023	8.07	26.9
Alloy steel (4140, annealed)	70	2,730	250	9,740	0.0023	6.28	22.4
Stainless 304	40	1,560	150	5,850	0.0016	2.50	9.36
Gray cast iron	80	3,120	250	9,740	0.0014	4.37	13.6
Titanium 6Al-4V	25	970	100	3,900	0.0012	1.16	4.68
Plastics (acetal)	300	11,690	500	19,490	0.0039	45.6	76.0

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, 3,510 RPM × 0.058 mm/rev = 205 mm/min.

Worked example: #40 drill in 1018 steel

HSS drill in low-carbon steel: 90 SFM.
RPM = 3.82 × 90 ÷ 0.0980 ≈ 3,510 RPM.
Feed for a 0.098 in drill in mild steel ≈ 0.0023 in/rev.
IPM = 3,510 × 0.0023 = 8.07 IPM.

Peck cycle by hole depth

#40 drill: depth and canned cycle
Depth	Cycle	Peck	Note
3×D = 0.294 in (7.5 mm)	G81 (no peck)	None	Up to 3×D a sharp drill clears chips on its own.
5×D = 0.490 in (12.4 mm)	G73 chip-break	1 × D	Chip-break pecks; full retract if chips pack (soft aluminum, stainless).
8×D = 0.784 in (19.9 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 #40 drill

4-48 — cut tap, 50% thread · tap speeds and feeds

Nearest drills

2.5 mm: 0.0984 in / 2.500 mm (+0.0004 in)
#39: 0.0995 in / 2.527 mm (+0.0015 in)
2.45 mm: 0.0965 in / 2.450 mm (-0.0015 in)
#41: 0.0960 in / 2.438 mm (-0.0020 in)

Drill speed calculator, prefilled for #40 Drill finder: sizes near #40 Number drill chart Decimal equivalent chart

Common questions

What is a #40 drill in decimal and mm?: 0.0980 in, or 2.489 mm; nearest fractional drill: 3/32" (0.0938 in, -0.0043 in); nearest metric drill: 2.5 mm (0.0984 in, +0.0004 in).
What RPM for a #40 drill in steel?: In low-carbon steel (1018) an HSS #40 drill (0.0980 in) runs about 3,510 RPM at 90 SFM; a carbide drill about 11,690 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
What feed for a #40 drill?: About 0.0023 in/rev in mild steel, 0.0022 in/rev in aluminum and 0.0016 in/rev in 304 stainless. At 3,510 RPM that is 8.07 IPM in steel (IPM = RPM × IPR).
What RPM for a #40 drill in aluminum?: 9,740 RPM with HSS (250 SFM) or up to 23,390 RPM with carbide (600 SFM), feeding about 0.0022 in/rev.
What tap uses a #40 drill?: 4-48 (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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