What is a 10.0 mm drill in decimal and mm?

0.3937 in, or 10.000 mm; nearest fractional drill: 25/64" (0.3906 in, -0.0031 in); nearest number / letter drill: Letter X (0.3970 in, +0.0033 in).

What RPM for a 10.0 mm drill in steel?

In low-carbon steel (1018) an HSS 10.0 mm drill (0.3937 in) runs about 870 RPM at 90 SFM; a carbide drill about 2,910 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.

What feed for a 10.0 mm drill?

About 0.0096 in/rev in mild steel, 0.0087 in/rev in aluminum and 0.0066 in/rev in 304 stainless. At 870 RPM that is 8.35 IPM in steel (IPM = RPM × IPR).

What RPM for a 10.0 mm drill in aluminum?

2,430 RPM with HSS (250 SFM) or up to 5,820 RPM with carbide (600 SFM), feeding about 0.0087 in/rev.

What size is a 10.0 mm drill?

0.3937 in / 10.00 mm. The nearest other drills are 25/64" (0.3906 in), Letter X (0.3970 in), 9.9 mm (0.3898 in).

10.0 mm drill size

A 10.0 mm metric drill is 0.3937 in (10.000 mm).

Decimal inch: 0.3937
Millimeters: 10.000
Nearest 1/64: 25/64" (+0.0031)
Type: metric drill

Nearest equivalents in other systems

Drills closest to 10.0 mm
System	Drill	Inch	mm	Difference
Fractional	25/64"	0.3906	9.922	-0.0031 in
Number / letter	Letter X	0.3970	10.084	+0.0033 in

Speeds and feeds: in mild steel an HSS drill starts at about 870 RPM and 0.0096 in/rev (8.35 IPM); in 6061 aluminum about 2,430 RPM.

10.0 mm drill speeds and feeds by material

Jobber-length twist drill, D = 0.3937 in. RPM = 3.82 × SFM ÷ D, rounded to 10. Feed per rev scales with diameter and material; IPM = RPM × IPR.

10.0 mm drilling speeds
Material	HSS SFM	HSS RPM	Carbide SFM	Carbide RPM	Feed (in/rev)	HSS IPM	Carbide IPM
Aluminum (6061)	250	2,430	600	5,820	0.0087	21.1	50.6
Brass / free-machining	150	1,460	400	3,880	0.0065	9.49	25.2
Low-carbon steel (1018)	90	870	300	2,910	0.0096	8.35	27.9
Alloy steel (4140, annealed)	70	680	250	2,430	0.0106	7.21	25.8
Stainless 304	40	390	150	1,460	0.0066	2.57	9.64
Gray cast iron	80	780	250	2,430	0.0068	5.30	16.5
Titanium 6Al-4V	25	240	100	970	0.0044	1.06	4.27
Plastics (acetal)	300	2,910	500	4,850	0.0051	14.8	24.7

Metric: Vc (m/min) = SFM × 0.3048; feed (mm/rev) = in/rev × 25.4. In steel, 870 RPM × 0.244 mm/rev = 212 mm/min.

Worked example: 10.0 mm drill in 1018 steel

HSS drill in low-carbon steel: 90 SFM.
RPM = 3.82 × 90 ÷ 0.3937 ≈ 870 RPM.
Feed for a 0.394 in drill in mild steel ≈ 0.0096 in/rev.
IPM = 870 × 0.0096 = 8.35 IPM.

Peck cycle by hole depth

10.0 mm drill: depth and canned cycle
Depth	Cycle	Peck	Note
3×D = 1.181 in (30 mm)	G81 (no peck)	None	Up to 3×D a sharp drill clears chips on its own.
5×D = 1.969 in (50 mm)	G73 chip-break	1 × D	Chip-break pecks; full retract if chips pack (soft aluminum, stainless).
8×D = 3.150 in (80 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 10.0 mm drill

No standard UNC, UNF or metric tap in our tables calls for a 10.0 mm drill. Use it for clearance, pilot or reamer prep holes.

Nearest drills

25/64": 0.3906 in / 9.922 mm (-0.0031 in)
Letter X: 0.3970 in / 10.084 mm (+0.0033 in)
9.9 mm: 0.3898 in / 9.900 mm (-0.0039 in)
10.1 mm: 0.3976 in / 10.100 mm (+0.0039 in)

Drill speed calculator, prefilled for 10.0 mm Drill finder: sizes near 10.0 mm Metric drill chart Decimal equivalent chart

Common questions

What is a 10.0 mm drill in decimal and mm?: 0.3937 in, or 10.000 mm; nearest fractional drill: 25/64" (0.3906 in, -0.0031 in); nearest number / letter drill: Letter X (0.3970 in, +0.0033 in).
What RPM for a 10.0 mm drill in steel?: In low-carbon steel (1018) an HSS 10.0 mm drill (0.3937 in) runs about 870 RPM at 90 SFM; a carbide drill about 2,910 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
What feed for a 10.0 mm drill?: About 0.0096 in/rev in mild steel, 0.0087 in/rev in aluminum and 0.0066 in/rev in 304 stainless. At 870 RPM that is 8.35 IPM in steel (IPM = RPM × IPR).
What RPM for a 10.0 mm drill in aluminum?: 2,430 RPM with HSS (250 SFM) or up to 5,820 RPM with carbide (600 SFM), feeding about 0.0087 in/rev.
What size is a 10.0 mm drill?: 0.3937 in / 10.00 mm. The nearest other drills are 25/64" (0.3906 in), Letter X (0.3970 in), 9.9 mm (0.3898 in).

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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