What is a 6.5 mm drill in decimal and mm?

0.2559 in, or 6.500 mm; nearest fractional drill: 1/4" (0.2500 in, -0.0059 in); nearest number / letter drill: Letter F (0.2570 in, +0.0011 in).

What RPM for a 6.5 mm drill in steel?

In low-carbon steel (1018) an HSS 6.5 mm drill (0.2559 in) runs about 1,340 RPM at 90 SFM; a carbide drill about 4,480 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.

What feed for a 6.5 mm drill?

About 0.0066 in/rev in mild steel, 0.0061 in/rev in aluminum and 0.0043 in/rev in 304 stainless. At 1,340 RPM that is 8.84 IPM in steel (IPM = RPM × IPR).

What RPM for a 6.5 mm drill in aluminum?

3,730 RPM with HSS (250 SFM) or up to 8,960 RPM with carbide (600 SFM), feeding about 0.0061 in/rev.

What size is a 6.5 mm drill?

0.2559 in / 6.500 mm. The nearest other drills are Letter F (0.2570 in), 6.6 mm (0.2598 in), 6.4 mm (0.2520 in).

6.5 mm drill size

A 6.5 mm metric drill is 0.2559 in (6.500 mm).

Decimal inch: 0.2559
Millimeters: 6.500
Nearest 1/64: 1/4" (+0.0059)
Type: metric drill

Nearest equivalents in other systems

Drills closest to 6.5 mm
System	Drill	Inch	mm	Difference
Fractional	1/4"	0.2500	6.350	-0.0059 in
Number / letter	Letter F	0.2570	6.528	+0.0011 in

Speeds and feeds: in mild steel an HSS drill starts at about 1,340 RPM and 0.0066 in/rev (8.84 IPM); in 6061 aluminum about 3,730 RPM.

6.5 mm drill speeds and feeds by material

Jobber-length twist drill, D = 0.2559 in. RPM = 3.82 × SFM ÷ D, rounded to 10. Feed per rev scales with diameter and material; IPM = RPM × IPR.

6.5 mm drilling speeds
Material	HSS SFM	HSS RPM	Carbide SFM	Carbide RPM	Feed (in/rev)	HSS IPM	Carbide IPM
Aluminum (6061)	250	3,730	600	8,960	0.0061	22.8	54.7
Brass / free-machining	150	2,240	400	5,970	0.0053	11.9	31.6
Low-carbon steel (1018)	90	1,340	300	4,480	0.0066	8.84	29.6
Alloy steel (4140, annealed)	70	1,040	250	3,730	0.0067	6.97	25.0
Stainless 304	40	600	150	2,240	0.0043	2.58	9.63
Gray cast iron	80	1,190	250	3,730	0.0046	5.47	17.2
Titanium 6Al-4V	25	370	100	1,490	0.0031	1.15	4.62
Plastics (acetal)	300	4,480	500	7,460	0.0040	17.9	29.8

Metric: Vc (m/min) = SFM × 0.3048; feed (mm/rev) = in/rev × 25.4. In steel, 1,340 RPM × 0.168 mm/rev = 225 mm/min.

Worked example: 6.5 mm drill in 1018 steel

HSS drill in low-carbon steel: 90 SFM.
RPM = 3.82 × 90 ÷ 0.2559 ≈ 1,340 RPM.
Feed for a 0.256 in drill in mild steel ≈ 0.0066 in/rev.
IPM = 1,340 × 0.0066 = 8.84 IPM.

Peck cycle by hole depth

6.5 mm drill: depth and canned cycle
Depth	Cycle	Peck	Note
3×D = 0.768 in (19.5 mm)	G81 (no peck)	None	Up to 3×D a sharp drill clears chips on its own.
5×D = 1.280 in (32.5 mm)	G73 chip-break	1 × D	Chip-break pecks; full retract if chips pack (soft aluminum, stainless).
8×D = 2.047 in (52 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 6.5 mm drill

No standard UNC, UNF or metric tap in our tables calls for a 6.5 mm drill. Use it for clearance, pilot or reamer prep holes.

Nearest drills

Letter F: 0.2570 in / 6.528 mm (+0.0011 in)
6.6 mm: 0.2598 in / 6.600 mm (+0.0039 in)
6.4 mm: 0.2520 in / 6.400 mm (-0.0039 in)
Letter G: 0.2610 in / 6.629 mm (+0.0051 in)

Drill speed calculator, prefilled for 6.5 mm Drill finder: sizes near 6.5 mm Metric drill chart Decimal equivalent chart

Common questions

What is a 6.5 mm drill in decimal and mm?: 0.2559 in, or 6.500 mm; nearest fractional drill: 1/4" (0.2500 in, -0.0059 in); nearest number / letter drill: Letter F (0.2570 in, +0.0011 in).
What RPM for a 6.5 mm drill in steel?: In low-carbon steel (1018) an HSS 6.5 mm drill (0.2559 in) runs about 1,340 RPM at 90 SFM; a carbide drill about 4,480 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
What feed for a 6.5 mm drill?: About 0.0066 in/rev in mild steel, 0.0061 in/rev in aluminum and 0.0043 in/rev in 304 stainless. At 1,340 RPM that is 8.84 IPM in steel (IPM = RPM × IPR).
What RPM for a 6.5 mm drill in aluminum?: 3,730 RPM with HSS (250 SFM) or up to 8,960 RPM with carbide (600 SFM), feeding about 0.0061 in/rev.
What size is a 6.5 mm drill?: 0.2559 in / 6.500 mm. The nearest other drills are Letter F (0.2570 in), 6.6 mm (0.2598 in), 6.4 mm (0.2520 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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