What is a #42 drill in decimal and mm?

0.0935 in, or 2.375 mm; nearest fractional drill: 3/32" (0.0938 in, +0.0003 in); nearest metric drill: 2.35 mm (0.0925 in, -0.0010 in).

What RPM for a #42 drill in steel?

In low-carbon steel (1018) an HSS #42 drill (0.0935 in) runs about 3,680 RPM at 90 SFM; a carbide drill about 12,260 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.

What feed for a #42 drill?

About 0.0022 in/rev in mild steel, 0.0021 in/rev in aluminum and 0.0015 in/rev in 304 stainless. At 3,680 RPM that is 8.10 IPM in steel (IPM = RPM × IPR).

What RPM for a #42 drill in aluminum?

10,210 RPM with HSS (250 SFM) or up to 24,510 RPM with carbide (600 SFM), feeding about 0.0021 in/rev.

What tap uses a #42 drill?

4-48 (cut tap, 75% thread); 2-64 (Helicoil / STI insert (#2-64×1D)).

#42 drill size

A #42 number (wire-gauge) drill is 0.0935 in (2.375 mm). It is the cut tap, 75% thread drill for 4-48.

Decimal inch: 0.0935
Millimeters: 2.375
Nearest 1/64: 3/32" (-0.0003)
Type: number (wire-gauge) drill

Nearest equivalents in other systems

Drills closest to #42
System	Drill	Inch	mm	Difference
Fractional	3/32"	0.0938	2.381	+0.0003 in
Metric	2.35 mm	0.0925	2.350	-0.0010 in

Speeds and feeds: in mild steel an HSS drill starts at about 3,680 RPM and 0.0022 in/rev (8.10 IPM); in 6061 aluminum about 10,210 RPM.

#42 drill speeds and feeds by material

Jobber-length twist drill, D = 0.0935 in. RPM = 3.82 × SFM ÷ D, rounded to 10. Feed per rev scales with diameter and material; IPM = RPM × IPR.

#42 drilling speeds
Material	HSS SFM	HSS RPM	Carbide SFM	Carbide RPM	Feed (in/rev)	HSS IPM	Carbide IPM
Aluminum (6061)	250	10,210	600	24,510	0.0021	21.4	51.5
Brass / free-machining	150	6,130	400	16,340	0.0018	11.0	29.4
Low-carbon steel (1018)	90	3,680	300	12,260	0.0022	8.10	27.0
Alloy steel (4140, annealed)	70	2,860	250	10,210	0.0022	6.29	22.5
Stainless 304	40	1,630	150	6,130	0.0015	2.44	9.20
Gray cast iron	80	3,270	250	10,210	0.0013	4.25	13.3
Titanium 6Al-4V	25	1,020	100	4,090	0.0012	1.22	4.91
Plastics (acetal)	300	12,260	500	20,430	0.0037	45.4	75.6

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, 3,680 RPM × 0.056 mm/rev = 206 mm/min.

Worked example: #42 drill in 1018 steel

HSS drill in low-carbon steel: 90 SFM.
RPM = 3.82 × 90 ÷ 0.0935 ≈ 3,680 RPM.
Feed for a 0.093 in drill in mild steel ≈ 0.0022 in/rev.
IPM = 3,680 × 0.0022 = 8.10 IPM.

Peck cycle by hole depth

#42 drill: depth and canned cycle
Depth	Cycle	Peck	Note
3×D = 0.281 in (7.1 mm)	G81 (no peck)	None	Up to 3×D a sharp drill clears chips on its own.
5×D = 0.468 in (11.9 mm)	G73 chip-break	1 × D	Chip-break pecks; full retract if chips pack (soft aluminum, stainless).
8×D = 0.748 in (19 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 #42 drill

4-48 — cut tap, 75% thread · tap speeds and feeds
2-64 — Helicoil / STI insert (#2-64×1D) · tap speeds and feeds

Nearest drills

3/32": 0.0938 in / 2.381 mm (+0.0003 in)
2.35 mm: 0.0925 in / 2.350 mm (-0.0010 in)
2.4 mm: 0.0945 in / 2.400 mm (+0.0010 in)
#41: 0.0960 in / 2.438 mm (+0.0025 in)

Drill speed calculator, prefilled for #42 Drill finder: sizes near #42 Number drill chart Decimal equivalent chart

Common questions

What is a #42 drill in decimal and mm?: 0.0935 in, or 2.375 mm; nearest fractional drill: 3/32" (0.0938 in, +0.0003 in); nearest metric drill: 2.35 mm (0.0925 in, -0.0010 in).
What RPM for a #42 drill in steel?: In low-carbon steel (1018) an HSS #42 drill (0.0935 in) runs about 3,680 RPM at 90 SFM; a carbide drill about 12,260 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
What feed for a #42 drill?: About 0.0022 in/rev in mild steel, 0.0021 in/rev in aluminum and 0.0015 in/rev in 304 stainless. At 3,680 RPM that is 8.10 IPM in steel (IPM = RPM × IPR).
What RPM for a #42 drill in aluminum?: 10,210 RPM with HSS (250 SFM) or up to 24,510 RPM with carbide (600 SFM), feeding about 0.0021 in/rev.
What tap uses a #42 drill?: 4-48 (cut tap, 75% thread); 2-64 (Helicoil / STI insert (#2-64×1D)).

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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