What is a 21/32" drill in decimal and mm?

0.6563 in, or 16.669 mm; nearest number / letter drill: Letter Z (0.4130 in, -0.2432 in); nearest metric drill: 16.75 mm (0.6594 in, +0.0032 in).

What RPM for a 21/32" drill in steel?

In low-carbon steel (1018) an HSS 21/32" drill (0.6563 in) runs about 520 RPM at 90 SFM; a carbide drill about 1,750 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.

What feed for a 21/32" drill?

About 0.0111 in/rev in mild steel, 0.0106 in/rev in aluminum and 0.0091 in/rev in 304 stainless. At 520 RPM that is 5.77 IPM in steel (IPM = RPM × IPR).

What RPM for a 21/32" drill in aluminum?

1,460 RPM with HSS (250 SFM) or up to 3,490 RPM with carbide (600 SFM), feeding about 0.0106 in/rev.

What tap uses a 21/32" drill?

3/4-10 (cut tap, 75% thread); 11/16-24 (cut tap, 50% thread).

21/32" drill size

A 21/32" fractional drill is 0.6563 in (16.669 mm). It is the cut tap, 75% thread drill for 3/4-10.

Decimal inch: 0.6563
Millimeters: 16.669
Nearest 1/64: 21/32" (+0.0000)
Type: fractional drill

Nearest equivalents in other systems

Drills closest to 21/32"
System	Drill	Inch	mm	Difference
Number / letter	Letter Z	0.4130	10.490	-0.2432 in
Metric	16.75 mm	0.6594	16.750	+0.0032 in

Speeds and feeds: in mild steel an HSS drill starts at about 520 RPM and 0.0111 in/rev (5.77 IPM); in 6061 aluminum about 1,460 RPM.

21/32" drill speeds and feeds by material

Jobber-length twist drill, D = 0.6563 in. RPM = 3.82 × SFM ÷ D, rounded to 10. Feed per rev scales with diameter and material; IPM = RPM × IPR.

21/32" drilling speeds
Material	HSS SFM	HSS RPM	Carbide SFM	Carbide RPM	Feed (in/rev)	HSS IPM	Carbide IPM
Aluminum (6061)	250	1,460	600	3,490	0.0106	15.5	37.0
Brass / free-machining	150	870	400	2,330	0.0087	7.57	20.3
Low-carbon steel (1018)	90	520	300	1,750	0.0111	5.77	19.4
Alloy steel (4140, annealed)	70	410	250	1,460	0.0118	4.84	17.2
Stainless 304	40	230	150	870	0.0091	2.09	7.92
Gray cast iron	80	470	250	1,460	0.0094	4.42	13.7
Titanium 6Al-4V	25	150	100	580	0.0053	0.80	3.07
Plastics (acetal)	300	1,750	500	2,910	0.0066	11.6	19.2

Metric: Vc (m/min) = SFM × 0.3048; feed (mm/rev) = in/rev × 25.4. In steel, 520 RPM × 0.282 mm/rev = 147 mm/min.

Worked example: 21/32" drill in 1018 steel

HSS drill in low-carbon steel: 90 SFM.
RPM = 3.82 × 90 ÷ 0.6563 ≈ 520 RPM.
Feed for a 0.656 in drill in mild steel ≈ 0.0111 in/rev.
IPM = 520 × 0.0111 = 5.77 IPM.

Peck cycle by hole depth

21/32" drill: depth and canned cycle
Depth	Cycle	Peck	Note
3×D = 1.969 in (50 mm)	G81 (no peck)	None	Up to 3×D a sharp drill clears chips on its own.
5×D = 3.281 in (83.3 mm)	G73 chip-break	1 × D	Chip-break pecks; full retract if chips pack (soft aluminum, stainless).
8×D = 5.250 in (133.4 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 21/32" drill

3/4-10 — cut tap, 75% thread · tap speeds and feeds
11/16-24 — cut tap, 50% thread

Nearest drills

16.75 mm: 0.6594 in / 16.750 mm (+0.0032 in)
16.5 mm: 0.6496 in / 16.500 mm (-0.0066 in)
17.0 mm: 0.6693 in / 17.000 mm (+0.0130 in)
41/64": 0.6406 in / 16.272 mm (-0.0156 in)

Drill speed calculator, prefilled for 21/32"Drill finder: sizes near 21/32"Fractional drill chart Decimal equivalent chart

Common questions

What is a 21/32" drill in decimal and mm?: 0.6563 in, or 16.669 mm; nearest number / letter drill: Letter Z (0.4130 in, -0.2432 in); nearest metric drill: 16.75 mm (0.6594 in, +0.0032 in).
What RPM for a 21/32" drill in steel?: In low-carbon steel (1018) an HSS 21/32" drill (0.6563 in) runs about 520 RPM at 90 SFM; a carbide drill about 1,750 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
What feed for a 21/32" drill?: About 0.0111 in/rev in mild steel, 0.0106 in/rev in aluminum and 0.0091 in/rev in 304 stainless. At 520 RPM that is 5.77 IPM in steel (IPM = RPM × IPR).
What RPM for a 21/32" drill in aluminum?: 1,460 RPM with HSS (250 SFM) or up to 3,490 RPM with carbide (600 SFM), feeding about 0.0106 in/rev.
What tap uses a 21/32" drill?: 3/4-10 (cut tap, 75% thread); 11/16-24 (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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