What is a 3.5 mm drill in decimal and mm?

0.1378 in, or 3.500 mm; nearest fractional drill: 9/64" (0.1406 in, +0.0028 in); nearest number / letter drill: #29 (0.1360 in, -0.0018 in).

What RPM for a 3.5 mm drill in steel?

In low-carbon steel (1018) an HSS 3.5 mm drill (0.1378 in) runs about 2,490 RPM at 90 SFM; a carbide drill about 8,320 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.

What feed for a 3.5 mm drill?

About 0.0033 in/rev in mild steel, 0.0032 in/rev in aluminum and 0.0022 in/rev in 304 stainless. At 2,490 RPM that is 8.22 IPM in steel (IPM = RPM × IPR).

What RPM for a 3.5 mm drill in aluminum?

6,930 RPM with HSS (250 SFM) or up to 16,630 RPM with carbide (600 SFM), feeding about 0.0032 in/rev.

What tap uses a 3.5 mm drill?

M4x0.5 (cut tap, 75% thread); M4×0.7 (cut tap, 50% thread).

3.5 mm drill size

A 3.5 mm metric drill is 0.1378 in (3.500 mm). It is the cut tap, 75% thread drill for M4x0.5.

Decimal inch: 0.1378
Millimeters: 3.500
Nearest 1/64: 9/64" (-0.0028)
Type: metric drill

Nearest equivalents in other systems

Drills closest to 3.5 mm
System	Drill	Inch	mm	Difference
Fractional	9/64"	0.1406	3.572	+0.0028 in
Number / letter	#29	0.1360	3.454	-0.0018 in

Speeds and feeds: in mild steel an HSS drill starts at about 2,490 RPM and 0.0033 in/rev (8.22 IPM); in 6061 aluminum about 6,930 RPM.

3.5 mm drill speeds and feeds by material

Jobber-length twist drill, D = 0.1378 in. RPM = 3.82 × SFM ÷ D, rounded to 10. Feed per rev scales with diameter and material; IPM = RPM × IPR.

3.5 mm drilling speeds
Material	HSS SFM	HSS RPM	Carbide SFM	Carbide RPM	Feed (in/rev)	HSS IPM	Carbide IPM
Aluminum (6061)	250	6,930	600	16,630	0.0032	22.2	53.2
Brass / free-machining	150	4,160	400	11,090	0.0027	11.2	29.9
Low-carbon steel (1018)	90	2,490	300	8,320	0.0033	8.22	27.5
Alloy steel (4140, annealed)	70	1,940	250	6,930	0.0033	6.40	22.9
Stainless 304	40	1,110	150	4,160	0.0022	2.44	9.15
Gray cast iron	80	2,220	250	6,930	0.0021	4.66	14.6
Titanium 6Al-4V	25	690	100	2,770	0.0017	1.17	4.71
Plastics (acetal)	300	8,320	500	13,860	0.0049	40.8	67.9

Metric: Vc (m/min) = SFM × 0.3048; feed (mm/rev) = in/rev × 25.4. In steel, 2,490 RPM × 0.084 mm/rev = 209 mm/min.

Worked example: 3.5 mm drill in 1018 steel

HSS drill in low-carbon steel: 90 SFM.
RPM = 3.82 × 90 ÷ 0.1378 ≈ 2,490 RPM.
Feed for a 0.138 in drill in mild steel ≈ 0.0033 in/rev.
IPM = 2,490 × 0.0033 = 8.22 IPM.

Peck cycle by hole depth

3.5 mm drill: depth and canned cycle
Depth	Cycle	Peck	Note
3×D = 0.413 in (10.5 mm)	G81 (no peck)	None	Up to 3×D a sharp drill clears chips on its own.
5×D = 0.689 in (17.5 mm)	G73 chip-break	1 × D	Chip-break pecks; full retract if chips pack (soft aluminum, stainless).
8×D = 1.102 in (28 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 3.5 mm drill

M4x0.5 — cut tap, 75% thread
M4×0.7 — cut tap, 50% thread · tap speeds and feeds

Nearest drills

#29: 0.1360 in / 3.454 mm (-0.0018 in)
#28: 0.1405 in / 3.569 mm (+0.0027 in)
9/64": 0.1406 in / 3.572 mm (+0.0028 in)
3.6 mm: 0.1417 in / 3.600 mm (+0.0039 in)

Drill speed calculator, prefilled for 3.5 mm Drill finder: sizes near 3.5 mm Metric drill chart Decimal equivalent chart

Common questions

What is a 3.5 mm drill in decimal and mm?: 0.1378 in, or 3.500 mm; nearest fractional drill: 9/64" (0.1406 in, +0.0028 in); nearest number / letter drill: #29 (0.1360 in, -0.0018 in).
What RPM for a 3.5 mm drill in steel?: In low-carbon steel (1018) an HSS 3.5 mm drill (0.1378 in) runs about 2,490 RPM at 90 SFM; a carbide drill about 8,320 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
What feed for a 3.5 mm drill?: About 0.0033 in/rev in mild steel, 0.0032 in/rev in aluminum and 0.0022 in/rev in 304 stainless. At 2,490 RPM that is 8.22 IPM in steel (IPM = RPM × IPR).
What RPM for a 3.5 mm drill in aluminum?: 6,930 RPM with HSS (250 SFM) or up to 16,630 RPM with carbide (600 SFM), feeding about 0.0032 in/rev.
What tap uses a 3.5 mm drill?: M4x0.5 (cut tap, 75% thread); M4×0.7 (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.

Free for machinists & programmers

Put your skills on a free talent profile

Machines, controls, certs and saved calculations in one profile shops can find.

Create free profile

For your shop

Bring shift handoffs to your shop

Stop losing job status between shifts. Every station's notes, counts and issues, handed off cleanly.

See shift handoffs