What is a 6.6 mm drill in decimal and mm?

0.2598 in, or 6.600 mm; nearest fractional drill: 17/64" (0.2656 in, +0.0058 in); nearest number / letter drill: Letter G (0.2610 in, +0.0012 in).

What RPM for a 6.6 mm drill in steel?

In low-carbon steel (1018) an HSS 6.6 mm drill (0.2598 in) runs about 1,320 RPM at 90 SFM; a carbide drill about 4,410 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.

What feed for a 6.6 mm drill?

About 0.0067 in/rev in mild steel, 0.0062 in/rev in aluminum and 0.0044 in/rev in 304 stainless. At 1,320 RPM that is 8.84 IPM in steel (IPM = RPM × IPR).

What RPM for a 6.6 mm drill in aluminum?

3,680 RPM with HSS (250 SFM) or up to 8,820 RPM with carbide (600 SFM), feeding about 0.0062 in/rev.

What tap uses a 6.6 mm drill?

M7x1 (form (roll) tap, 65% thread).

6.6 mm drill size

A 6.6 mm metric drill is 0.2598 in (6.600 mm). It is the form (roll) tap, 65% thread drill for M7x1.

Decimal inch: 0.2598
Millimeters: 6.600
Nearest 1/64: 17/64" (-0.0058)
Type: metric drill

Nearest equivalents in other systems

Drills closest to 6.6 mm
System	Drill	Inch	mm	Difference
Fractional	17/64"	0.2656	6.747	+0.0058 in
Number / letter	Letter G	0.2610	6.629	+0.0012 in

Speeds and feeds: in mild steel an HSS drill starts at about 1,320 RPM and 0.0067 in/rev (8.84 IPM); in 6061 aluminum about 3,680 RPM.

6.6 mm drill speeds and feeds by material

Jobber-length twist drill, D = 0.2598 in. RPM = 3.82 × SFM ÷ D, rounded to 10. Feed per rev scales with diameter and material; IPM = RPM × IPR.

6.6 mm drilling speeds
Material	HSS SFM	HSS RPM	Carbide SFM	Carbide RPM	Feed (in/rev)	HSS IPM	Carbide IPM
Aluminum (6061)	250	3,680	600	8,820	0.0062	22.8	54.7
Brass / free-machining	150	2,210	400	5,880	0.0053	11.7	31.2
Low-carbon steel (1018)	90	1,320	300	4,410	0.0067	8.84	29.6
Alloy steel (4140, annealed)	70	1,030	250	3,680	0.0068	7.00	25.0
Stainless 304	40	590	150	2,210	0.0044	2.60	9.72
Gray cast iron	80	1,180	250	3,680	0.0047	5.55	17.3
Titanium 6Al-4V	25	370	100	1,470	0.0031	1.15	4.56
Plastics (acetal)	300	4,410	500	7,350	0.0041	18.1	30.1

Metric: Vc (m/min) = SFM × 0.3048; feed (mm/rev) = in/rev × 25.4. In steel, 1,320 RPM × 0.170 mm/rev = 225 mm/min.

Worked example: 6.6 mm drill in 1018 steel

HSS drill in low-carbon steel: 90 SFM.
RPM = 3.82 × 90 ÷ 0.2598 ≈ 1,320 RPM.
Feed for a 0.260 in drill in mild steel ≈ 0.0067 in/rev.
IPM = 1,320 × 0.0067 = 8.84 IPM.

Peck cycle by hole depth

6.6 mm drill: depth and canned cycle
Depth	Cycle	Peck	Note
3×D = 0.780 in (19.8 mm)	G81 (no peck)	None	Up to 3×D a sharp drill clears chips on its own.
5×D = 1.299 in (33 mm)	G73 chip-break	1 × D	Chip-break pecks; full retract if chips pack (soft aluminum, stainless).
8×D = 2.079 in (52.8 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 6.6 mm drill

M7x1 — form (roll) tap, 65% thread · tap speeds and feeds

Nearest drills

Letter G: 0.2610 in / 6.629 mm (+0.0012 in)
Letter F: 0.2570 in / 6.528 mm (-0.0028 in)
6.5 mm: 0.2559 in / 6.500 mm (-0.0039 in)
6.7 mm: 0.2638 in / 6.700 mm (+0.0039 in)

Drill speed calculator, prefilled for 6.6 mm Drill finder: sizes near 6.6 mm Metric drill chart Decimal equivalent chart

Common questions

What is a 6.6 mm drill in decimal and mm?: 0.2598 in, or 6.600 mm; nearest fractional drill: 17/64" (0.2656 in, +0.0058 in); nearest number / letter drill: Letter G (0.2610 in, +0.0012 in).
What RPM for a 6.6 mm drill in steel?: In low-carbon steel (1018) an HSS 6.6 mm drill (0.2598 in) runs about 1,320 RPM at 90 SFM; a carbide drill about 4,410 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
What feed for a 6.6 mm drill?: About 0.0067 in/rev in mild steel, 0.0062 in/rev in aluminum and 0.0044 in/rev in 304 stainless. At 1,320 RPM that is 8.84 IPM in steel (IPM = RPM × IPR).
What RPM for a 6.6 mm drill in aluminum?: 3,680 RPM with HSS (250 SFM) or up to 8,820 RPM with carbide (600 SFM), feeding about 0.0062 in/rev.
What tap uses a 6.6 mm drill?: M7x1 (form (roll) tap, 65% 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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