What is a 10.9 mm drill in decimal and mm?

0.4291 in, or 10.900 mm; nearest fractional drill: 27/64" (0.4219 in, -0.0073 in); nearest number / letter drill: Letter Z (0.4130 in, -0.0161 in).

What RPM for a 10.9 mm drill in steel?

In low-carbon steel (1018) an HSS 10.9 mm drill (0.4291 in) runs about 800 RPM at 90 SFM; a carbide drill about 2,670 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.

What feed for a 10.9 mm drill?

About 0.0099 in/rev in mild steel, 0.0091 in/rev in aluminum and 0.0072 in/rev in 304 stainless. At 800 RPM that is 7.92 IPM in steel (IPM = RPM × IPR).

What RPM for a 10.9 mm drill in aluminum?

2,230 RPM with HSS (250 SFM) or up to 5,340 RPM with carbide (600 SFM), feeding about 0.0091 in/rev.

What tap uses a 10.9 mm drill?

M12×1.75 (cut tap, 50% thread).

10.9 mm drill size

A 10.9 mm metric drill is 0.4291 in (10.900 mm). It is the cut tap, 50% thread drill for M12×1.75.

Decimal inch: 0.4291
Millimeters: 10.900
Nearest 1/64: 27/64" (+0.0073)
Type: metric drill

Nearest equivalents in other systems

Drills closest to 10.9 mm
System	Drill	Inch	mm	Difference
Fractional	27/64"	0.4219	10.716	-0.0073 in
Number / letter	Letter Z	0.4130	10.490	-0.0161 in

Speeds and feeds: in mild steel an HSS drill starts at about 800 RPM and 0.0099 in/rev (7.92 IPM); in 6061 aluminum about 2,230 RPM.

10.9 mm drill speeds and feeds by material

Jobber-length twist drill, D = 0.4291 in. RPM = 3.82 × SFM ÷ D, rounded to 10. Feed per rev scales with diameter and material; IPM = RPM × IPR.

10.9 mm drilling speeds
Material	HSS SFM	HSS RPM	Carbide SFM	Carbide RPM	Feed (in/rev)	HSS IPM	Carbide IPM
Aluminum (6061)	250	2,230	600	5,340	0.0091	20.3	48.6
Brass / free-machining	150	1,340	400	3,560	0.0071	9.51	25.3
Low-carbon steel (1018)	90	800	300	2,670	0.0099	7.92	26.4
Alloy steel (4140, annealed)	70	620	250	2,230	0.0109	6.76	24.3
Stainless 304	40	360	150	1,340	0.0072	2.59	9.65
Gray cast iron	80	710	250	2,230	0.0074	5.25	16.5
Titanium 6Al-4V	25	220	100	890	0.0046	1.01	4.09
Plastics (acetal)	300	2,670	500	4,450	0.0054	14.4	24.0

Metric: Vc (m/min) = SFM × 0.3048; feed (mm/rev) = in/rev × 25.4. In steel, 800 RPM × 0.251 mm/rev = 201 mm/min.

Worked example: 10.9 mm drill in 1018 steel

HSS drill in low-carbon steel: 90 SFM.
RPM = 3.82 × 90 ÷ 0.4291 ≈ 800 RPM.
Feed for a 0.429 in drill in mild steel ≈ 0.0099 in/rev.
IPM = 800 × 0.0099 = 7.92 IPM.

Peck cycle by hole depth

10.9 mm drill: depth and canned cycle
Depth	Cycle	Peck	Note
3×D = 1.287 in (32.7 mm)	G81 (no peck)	None	Up to 3×D a sharp drill clears chips on its own.
5×D = 2.146 in (54.5 mm)	G73 chip-break	1 × D	Chip-break pecks; full retract if chips pack (soft aluminum, stainless).
8×D = 3.433 in (87.2 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 10.9 mm drill

M12×1.75 — cut tap, 50% thread · tap speeds and feeds

Nearest drills

10.8 mm: 0.4252 in / 10.800 mm (-0.0039 in)
11.0 mm: 0.4331 in / 11.000 mm (+0.0039 in)
27/64": 0.4219 in / 10.716 mm (-0.0073 in)
10.7 mm: 0.4213 in / 10.700 mm (-0.0079 in)

Drill speed calculator, prefilled for 10.9 mm Drill finder: sizes near 10.9 mm Metric drill chart Decimal equivalent chart

Common questions

What is a 10.9 mm drill in decimal and mm?: 0.4291 in, or 10.900 mm; nearest fractional drill: 27/64" (0.4219 in, -0.0073 in); nearest number / letter drill: Letter Z (0.4130 in, -0.0161 in).
What RPM for a 10.9 mm drill in steel?: In low-carbon steel (1018) an HSS 10.9 mm drill (0.4291 in) runs about 800 RPM at 90 SFM; a carbide drill about 2,670 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
What feed for a 10.9 mm drill?: About 0.0099 in/rev in mild steel, 0.0091 in/rev in aluminum and 0.0072 in/rev in 304 stainless. At 800 RPM that is 7.92 IPM in steel (IPM = RPM × IPR).
What RPM for a 10.9 mm drill in aluminum?: 2,230 RPM with HSS (250 SFM) or up to 5,340 RPM with carbide (600 SFM), feeding about 0.0091 in/rev.
What tap uses a 10.9 mm drill?: M12×1.75 (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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