What is a 27/32" drill in decimal and mm?

0.8438 in, or 21.431 mm; nearest number / letter drill: Letter Z (0.4130 in, -0.4308 in); nearest metric drill: 21.5 mm (0.8465 in, +0.0027 in).

What RPM for a 27/32" drill in steel?

In low-carbon steel (1018) an HSS 27/32" drill (0.8438 in) runs about 410 RPM at 90 SFM; a carbide drill about 1,360 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.

What feed for a 27/32" drill?

About 0.0119 in/rev in mild steel, 0.0118 in/rev in aluminum and 0.0099 in/rev in 304 stainless. At 410 RPM that is 4.88 IPM in steel (IPM = RPM × IPR).

What RPM for a 27/32" drill in aluminum?

1,130 RPM with HSS (250 SFM) or up to 2,720 RPM with carbide (600 SFM), feeding about 0.0118 in/rev.

What tap uses a 27/32" drill?

7/8-14 (form (roll) tap, 65% thread); 7/8-20 (cut tap, 50% thread).

27/32" drill size

A 27/32" fractional drill is 0.8438 in (21.431 mm). It is the form (roll) tap, 65% thread drill for 7/8-14.

Decimal inch: 0.8438
Millimeters: 21.431
Nearest 1/64: 27/32" (+0.0000)
Type: fractional drill

Nearest equivalents in other systems

Drills closest to 27/32"
System	Drill	Inch	mm	Difference
Number / letter	Letter Z	0.4130	10.490	-0.4308 in
Metric	21.5 mm	0.8465	21.500	+0.0027 in

Speeds and feeds: in mild steel an HSS drill starts at about 410 RPM and 0.0119 in/rev (4.88 IPM); in 6061 aluminum about 1,130 RPM.

27/32" drill speeds and feeds by material

Jobber-length twist drill, D = 0.8438 in. RPM = 3.82 × SFM ÷ D, rounded to 10. Feed per rev scales with diameter and material; IPM = RPM × IPR.

27/32" drilling speeds
Material	HSS SFM	HSS RPM	Carbide SFM	Carbide RPM	Feed (in/rev)	HSS IPM	Carbide IPM
Aluminum (6061)	250	1,130	600	2,720	0.0118	13.3	32.1
Brass / free-machining	150	680	400	1,810	0.0094	6.39	17.0
Low-carbon steel (1018)	90	410	300	1,360	0.0119	4.88	16.2
Alloy steel (4140, annealed)	70	320	250	1,130	0.0124	3.97	14.0
Stainless 304	40	180	150	680	0.0099	1.78	6.73
Gray cast iron	80	360	250	1,130	0.0104	3.74	11.8
Titanium 6Al-4V	25	110	100	450	0.0057	0.63	2.57
Plastics (acetal)	300	1,360	500	2,260	0.0074	10.1	16.7

Metric: Vc (m/min) = SFM × 0.3048; feed (mm/rev) = in/rev × 25.4. In steel, 410 RPM × 0.302 mm/rev = 124 mm/min.

Worked example: 27/32" drill in 1018 steel

HSS drill in low-carbon steel: 90 SFM.
RPM = 3.82 × 90 ÷ 0.8438 ≈ 410 RPM.
Feed for a 0.844 in drill in mild steel ≈ 0.0119 in/rev.
IPM = 410 × 0.0119 = 4.88 IPM.

Peck cycle by hole depth

27/32" drill: depth and canned cycle
Depth	Cycle	Peck	Note
3×D = 2.531 in (64.3 mm)	G81 (no peck)	None	Up to 3×D a sharp drill clears chips on its own.
5×D = 4.219 in (107.2 mm)	G73 chip-break	1 × D	Chip-break pecks; full retract if chips pack (soft aluminum, stainless).
8×D = 6.750 in (171.4 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 27/32" drill

7/8-14 — form (roll) tap, 65% thread · tap speeds and feeds
7/8-20 — cut tap, 50% thread

Nearest drills

21.5 mm: 0.8465 in / 21.500 mm (+0.0027 in)
21.25 mm: 0.8366 in / 21.250 mm (-0.0071 in)
21.75 mm: 0.8563 in / 21.750 mm (+0.0126 in)
53/64": 0.8281 in / 21.034 mm (-0.0156 in)

Drill speed calculator, prefilled for 27/32"Drill finder: sizes near 27/32"Fractional drill chart Decimal equivalent chart

Common questions

What is a 27/32" drill in decimal and mm?: 0.8438 in, or 21.431 mm; nearest number / letter drill: Letter Z (0.4130 in, -0.4308 in); nearest metric drill: 21.5 mm (0.8465 in, +0.0027 in).
What RPM for a 27/32" drill in steel?: In low-carbon steel (1018) an HSS 27/32" drill (0.8438 in) runs about 410 RPM at 90 SFM; a carbide drill about 1,360 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
What feed for a 27/32" drill?: About 0.0119 in/rev in mild steel, 0.0118 in/rev in aluminum and 0.0099 in/rev in 304 stainless. At 410 RPM that is 4.88 IPM in steel (IPM = RPM × IPR).
What RPM for a 27/32" drill in aluminum?: 1,130 RPM with HSS (250 SFM) or up to 2,720 RPM with carbide (600 SFM), feeding about 0.0118 in/rev.
What tap uses a 27/32" drill?: 7/8-14 (form (roll) tap, 65% thread); 7/8-20 (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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