What is a 61/64" drill in decimal and mm?

0.9531 in, or 24.209 mm; nearest number / letter drill: Letter Z (0.4130 in, -0.5401 in); nearest metric drill: 24.25 mm (0.9547 in, +0.0016 in).

What RPM for a 61/64" drill in steel?

In low-carbon steel (1018) an HSS 61/64" drill (0.9531 in) runs about 360 RPM at 90 SFM; a carbide drill about 1,200 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.

What feed for a 61/64" drill?

About 0.0123 in/rev in mild steel, 0.0126 in/rev in aluminum and 0.0103 in/rev in 304 stainless. At 360 RPM that is 4.43 IPM in steel (IPM = RPM × IPR).

What RPM for a 61/64" drill in aluminum?

1,000 RPM with HSS (250 SFM) or up to 2,400 RPM with carbide (600 SFM), feeding about 0.0126 in/rev.

What tap uses a 61/64" drill?

1-20 (cut tap, 75% thread); 1-12 (cut tap, 50% thread).

61/64" drill size

A 61/64" fractional drill is 0.9531 in (24.209 mm). It is the cut tap, 75% thread drill for 1-20.

Decimal inch: 0.9531
Millimeters: 24.209
Nearest 1/64: 61/64" (+0.0000)
Type: fractional drill

Nearest equivalents in other systems

Drills closest to 61/64"
System	Drill	Inch	mm	Difference
Number / letter	Letter Z	0.4130	10.490	-0.5401 in
Metric	24.25 mm	0.9547	24.250	+0.0016 in

Speeds and feeds: in mild steel an HSS drill starts at about 360 RPM and 0.0123 in/rev (4.43 IPM); in 6061 aluminum about 1,000 RPM.

61/64" drill speeds and feeds by material

Jobber-length twist drill, D = 0.9531 in. RPM = 3.82 × SFM ÷ D, rounded to 10. Feed per rev scales with diameter and material; IPM = RPM × IPR.

61/64" drilling speeds
Material	HSS SFM	HSS RPM	Carbide SFM	Carbide RPM	Feed (in/rev)	HSS IPM	Carbide IPM
Aluminum (6061)	250	1,000	600	2,400	0.0126	12.6	30.2
Brass / free-machining	150	600	400	1,600	0.0098	5.88	15.7
Low-carbon steel (1018)	90	360	300	1,200	0.0123	4.43	14.8
Alloy steel (4140, annealed)	70	280	250	1,000	0.0128	3.58	12.8
Stainless 304	40	160	150	600	0.0103	1.65	6.18
Gray cast iron	80	320	250	1,000	0.0108	3.46	10.8
Titanium 6Al-4V	25	100	100	400	0.0059	0.59	2.36
Plastics (acetal)	300	1,200	500	2,000	0.0078	9.36	15.6

Metric: Vc (m/min) = SFM × 0.3048; feed (mm/rev) = in/rev × 25.4. In steel, 360 RPM × 0.312 mm/rev = 112 mm/min.

Worked example: 61/64" drill in 1018 steel

HSS drill in low-carbon steel: 90 SFM.
RPM = 3.82 × 90 ÷ 0.9531 ≈ 360 RPM.
Feed for a 0.953 in drill in mild steel ≈ 0.0123 in/rev.
IPM = 360 × 0.0123 = 4.43 IPM.

Peck cycle by hole depth

61/64" drill: depth and canned cycle
Depth	Cycle	Peck	Note
3×D = 2.859 in (72.6 mm)	G81 (no peck)	None	Up to 3×D a sharp drill clears chips on its own.
5×D = 4.766 in (121 mm)	G73 chip-break	1 × D	Chip-break pecks; full retract if chips pack (soft aluminum, stainless).
8×D = 7.625 in (193.7 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 61/64" drill

1-20 — cut tap, 75% thread
1-12 — cut tap, 50% thread · tap speeds and feeds

Nearest drills

24.25 mm: 0.9547 in / 24.250 mm (+0.0016 in)
24.0 mm: 0.9449 in / 24.000 mm (-0.0082 in)
24.5 mm: 0.9646 in / 24.500 mm (+0.0115 in)
15/16": 0.9375 in / 23.813 mm (-0.0156 in)

Drill speed calculator, prefilled for 61/64"Drill finder: sizes near 61/64"Fractional drill chart Decimal equivalent chart

Common questions

What is a 61/64" drill in decimal and mm?: 0.9531 in, or 24.209 mm; nearest number / letter drill: Letter Z (0.4130 in, -0.5401 in); nearest metric drill: 24.25 mm (0.9547 in, +0.0016 in).
What RPM for a 61/64" drill in steel?: In low-carbon steel (1018) an HSS 61/64" drill (0.9531 in) runs about 360 RPM at 90 SFM; a carbide drill about 1,200 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
What feed for a 61/64" drill?: About 0.0123 in/rev in mild steel, 0.0126 in/rev in aluminum and 0.0103 in/rev in 304 stainless. At 360 RPM that is 4.43 IPM in steel (IPM = RPM × IPR).
What RPM for a 61/64" drill in aluminum?: 1,000 RPM with HSS (250 SFM) or up to 2,400 RPM with carbide (600 SFM), feeding about 0.0126 in/rev.
What tap uses a 61/64" drill?: 1-20 (cut tap, 75% thread); 1-12 (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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