What is a #20 drill in decimal and mm?

0.1610 in, or 4.089 mm; nearest fractional drill: 5/32" (0.1563 in, -0.0047 in); nearest metric drill: 4.1 mm (0.1614 in, +0.0004 in).

What RPM for a #20 drill in steel?

In low-carbon steel (1018) an HSS #20 drill (0.1610 in) runs about 2,140 RPM at 90 SFM; a carbide drill about 7,120 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.

What feed for a #20 drill?

About 0.0040 in/rev in mild steel, 0.0038 in/rev in aluminum and 0.0026 in/rev in 304 stainless. At 2,140 RPM that is 8.56 IPM in steel (IPM = RPM × IPR).

What RPM for a #20 drill in aluminum?

5,930 RPM with HSS (250 SFM) or up to 14,230 RPM with carbide (600 SFM), feeding about 0.0038 in/rev.

#20 drill size

A #20 number (wire-gauge) drill is 0.1610 in (4.089 mm). It is the cut tap, 50% thread drill for 10-24.

Decimal inch: 0.1610
Millimeters: 4.089
Nearest 1/64: 5/32" (+0.0048)
Type: number (wire-gauge) drill

Nearest equivalents in other systems

Drills closest to #20
System	Drill	Inch	mm	Difference
Fractional	5/32"	0.1563	3.969	-0.0047 in
Metric	4.1 mm	0.1614	4.100	+0.0004 in

Speeds and feeds: in mild steel an HSS drill starts at about 2,140 RPM and 0.0040 in/rev (8.56 IPM); in 6061 aluminum about 5,930 RPM.

#20 drill speeds and feeds by material

Jobber-length twist drill, D = 0.1610 in. RPM = 3.82 × SFM ÷ D, rounded to 10. Feed per rev scales with diameter and material; IPM = RPM × IPR.

#20 drilling speeds
Material	HSS SFM	HSS RPM	Carbide SFM	Carbide RPM	Feed (in/rev)	HSS IPM	Carbide IPM
Aluminum (6061)	250	5,930	600	14,230	0.0038	22.5	54.1
Brass / free-machining	150	3,560	400	9,490	0.0032	11.4	30.4
Low-carbon steel (1018)	90	2,140	300	7,120	0.0040	8.56	28.5
Alloy steel (4140, annealed)	70	1,660	250	5,930	0.0040	6.64	23.7
Stainless 304	40	950	150	3,560	0.0026	2.47	9.26
Gray cast iron	80	1,900	250	5,930	0.0026	4.94	15.4
Titanium 6Al-4V	25	590	100	2,370	0.0020	1.18	4.74
Plastics (acetal)	300	7,120	500	11,860	0.0047	33.5	55.7

Metric: Vc (m/min) = SFM × 0.3048; feed (mm/rev) = in/rev × 25.4. In steel, 2,140 RPM × 0.102 mm/rev = 217 mm/min.

Worked example: #20 drill in 1018 steel

HSS drill in low-carbon steel: 90 SFM.
RPM = 3.82 × 90 ÷ 0.1610 ≈ 2,140 RPM.
Feed for a 0.161 in drill in mild steel ≈ 0.0040 in/rev.
IPM = 2,140 × 0.0040 = 8.56 IPM.

Peck cycle by hole depth

#20 drill: depth and canned cycle
Depth	Cycle	Peck	Note
3×D = 0.483 in (12.3 mm)	G81 (no peck)	None	Up to 3×D a sharp drill clears chips on its own.
5×D = 0.805 in (20.4 mm)	G73 chip-break	1 × D	Chip-break pecks; full retract if chips pack (soft aluminum, stainless).
8×D = 1.288 in (32.7 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 #20 drill

10-24 — cut tap, 50% thread · tap speeds and feeds

Nearest drills

4.1 mm: 0.1614 in / 4.100 mm (+0.0004 in)
#21: 0.1590 in / 4.039 mm (-0.0020 in)
4.0 mm: 0.1575 in / 4.000 mm (-0.0035 in)
#22: 0.1570 in / 3.988 mm (-0.0040 in)

Drill speed calculator, prefilled for #20 Drill finder: sizes near #20 Number drill chart Decimal equivalent chart

Common questions

What is a #20 drill in decimal and mm?: 0.1610 in, or 4.089 mm; nearest fractional drill: 5/32" (0.1563 in, -0.0047 in); nearest metric drill: 4.1 mm (0.1614 in, +0.0004 in).
What RPM for a #20 drill in steel?: In low-carbon steel (1018) an HSS #20 drill (0.1610 in) runs about 2,140 RPM at 90 SFM; a carbide drill about 7,120 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
What feed for a #20 drill?: About 0.0040 in/rev in mild steel, 0.0038 in/rev in aluminum and 0.0026 in/rev in 304 stainless. At 2,140 RPM that is 8.56 IPM in steel (IPM = RPM × IPR).
What RPM for a #20 drill in aluminum?: 5,930 RPM with HSS (250 SFM) or up to 14,230 RPM with carbide (600 SFM), feeding about 0.0038 in/rev.
What tap uses a #20 drill?: 10-24 (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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