What is a 59/64" drill in decimal and mm?

0.9219 in, or 23.416 mm; nearest number / letter drill: Letter Z (0.4130 in, -0.5089 in); nearest metric drill: 23.5 mm (0.9252 in, +0.0033 in).

What RPM for a 59/64" drill in steel?

In low-carbon steel (1018) an HSS 59/64" drill (0.9219 in) runs about 370 RPM at 90 SFM; a carbide drill about 1,240 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.

What feed for a 59/64" drill?

About 0.0122 in/rev in mild steel, 0.0124 in/rev in aluminum and 0.0102 in/rev in 304 stainless. At 370 RPM that is 4.51 IPM in steel (IPM = RPM × IPR).

What RPM for a 59/64" drill in aluminum?

1,040 RPM with HSS (250 SFM) or up to 2,490 RPM with carbide (600 SFM), feeding about 0.0124 in/rev.

What tap uses a 59/64" drill?

1-12 (cut tap, 75% thread); 15/16-20 (form (roll) tap, 65% thread); 1"-8 (cut tap, 50% thread).

59/64" drill size

A 59/64" fractional drill is 0.9219 in (23.416 mm). It is the cut tap, 75% thread drill for 1-12.

Decimal inch: 0.9219
Millimeters: 23.416
Nearest 1/64: 59/64" (+0.0000)
Type: fractional drill

Nearest equivalents in other systems

Drills closest to 59/64"
System	Drill	Inch	mm	Difference
Number / letter	Letter Z	0.4130	10.490	-0.5089 in
Metric	23.5 mm	0.9252	23.500	+0.0033 in

Speeds and feeds: in mild steel an HSS drill starts at about 370 RPM and 0.0122 in/rev (4.51 IPM); in 6061 aluminum about 1,040 RPM.

59/64" drill speeds and feeds by material

Jobber-length twist drill, D = 0.9219 in. RPM = 3.82 × SFM ÷ D, rounded to 10. Feed per rev scales with diameter and material; IPM = RPM × IPR.

59/64" drilling speeds
Material	HSS SFM	HSS RPM	Carbide SFM	Carbide RPM	Feed (in/rev)	HSS IPM	Carbide IPM
Aluminum (6061)	250	1,040	600	2,490	0.0124	12.9	30.9
Brass / free-machining	150	620	400	1,660	0.0097	6.01	16.1
Low-carbon steel (1018)	90	370	300	1,240	0.0122	4.51	15.1
Alloy steel (4140, annealed)	70	290	250	1,040	0.0127	3.68	13.2
Stainless 304	40	170	150	620	0.0102	1.73	6.32
Gray cast iron	80	330	250	1,040	0.0107	3.53	11.1
Titanium 6Al-4V	25	100	100	410	0.0058	0.58	2.38
Plastics (acetal)	300	1,240	500	2,070	0.0077	9.55	15.9

Metric: Vc (m/min) = SFM × 0.3048; feed (mm/rev) = in/rev × 25.4. In steel, 370 RPM × 0.310 mm/rev = 115 mm/min.

Worked example: 59/64" drill in 1018 steel

HSS drill in low-carbon steel: 90 SFM.
RPM = 3.82 × 90 ÷ 0.9219 ≈ 370 RPM.
Feed for a 0.922 in drill in mild steel ≈ 0.0122 in/rev.
IPM = 370 × 0.0122 = 4.51 IPM.

Peck cycle by hole depth

59/64" drill: depth and canned cycle
Depth	Cycle	Peck	Note
3×D = 2.766 in (70.2 mm)	G81 (no peck)	None	Up to 3×D a sharp drill clears chips on its own.
5×D = 4.609 in (117.1 mm)	G73 chip-break	1 × D	Chip-break pecks; full retract if chips pack (soft aluminum, stainless).
8×D = 7.375 in (187.3 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 59/64" drill

1-12 — cut tap, 75% thread · tap speeds and feeds
15/16-20 — form (roll) tap, 65% thread
1"-8 — cut tap, 50% thread · tap speeds and feeds

Nearest drills

23.5 mm: 0.9252 in / 23.500 mm (+0.0033 in)
23.25 mm: 0.9153 in / 23.250 mm (-0.0065 in)
23.75 mm: 0.9350 in / 23.750 mm (+0.0132 in)
29/32": 0.9063 in / 23.019 mm (-0.0156 in)

Drill speed calculator, prefilled for 59/64"Drill finder: sizes near 59/64"Fractional drill chart Decimal equivalent chart

Common questions

What is a 59/64" drill in decimal and mm?: 0.9219 in, or 23.416 mm; nearest number / letter drill: Letter Z (0.4130 in, -0.5089 in); nearest metric drill: 23.5 mm (0.9252 in, +0.0033 in).
What RPM for a 59/64" drill in steel?: In low-carbon steel (1018) an HSS 59/64" drill (0.9219 in) runs about 370 RPM at 90 SFM; a carbide drill about 1,240 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
What feed for a 59/64" drill?: About 0.0122 in/rev in mild steel, 0.0124 in/rev in aluminum and 0.0102 in/rev in 304 stainless. At 370 RPM that is 4.51 IPM in steel (IPM = RPM × IPR).
What RPM for a 59/64" drill in aluminum?: 1,040 RPM with HSS (250 SFM) or up to 2,490 RPM with carbide (600 SFM), feeding about 0.0124 in/rev.
What tap uses a 59/64" drill?: 1-12 (cut tap, 75% thread); 15/16-20 (form (roll) tap, 65% thread); 1"-8 (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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