What is a 31/32" drill in decimal and mm?

0.9688 in, or 24.606 mm; nearest number / letter drill: Letter Z (0.4130 in, -0.5557 in); nearest metric drill: 24.5 mm (0.9646 in, -0.0042 in).

What RPM for a 31/32" drill in steel?

In low-carbon steel (1018) an HSS 31/32" drill (0.9688 in) runs about 350 RPM at 90 SFM; a carbide drill about 1,180 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.

What feed for a 31/32" drill?

About 0.0124 in/rev in mild steel, 0.0128 in/rev in aluminum and 0.0104 in/rev in 304 stainless. At 350 RPM that is 4.34 IPM in steel (IPM = RPM × IPR).

What RPM for a 31/32" drill in aluminum?

990 RPM with HSS (250 SFM) or up to 2,370 RPM with carbide (600 SFM), feeding about 0.0128 in/rev.

What tap uses a 31/32" drill?

1-12 (form (roll) tap, 65% thread); 1-20 (cut tap, 50% thread).

31/32" drill size

A 31/32" fractional drill is 0.9688 in (24.606 mm). It is the form (roll) tap, 65% thread drill for 1-12.

Decimal inch: 0.9688
Millimeters: 24.606
Nearest 1/64: 31/32" (+0.0000)
Type: fractional drill

Nearest equivalents in other systems

Drills closest to 31/32"
System	Drill	Inch	mm	Difference
Number / letter	Letter Z	0.4130	10.490	-0.5557 in
Metric	24.5 mm	0.9646	24.500	-0.0042 in

Speeds and feeds: in mild steel an HSS drill starts at about 350 RPM and 0.0124 in/rev (4.34 IPM); in 6061 aluminum about 990 RPM.

31/32" drill speeds and feeds by material

Jobber-length twist drill, D = 0.9688 in. RPM = 3.82 × SFM ÷ D, rounded to 10. Feed per rev scales with diameter and material; IPM = RPM × IPR.

31/32" drilling speeds
Material	HSS SFM	HSS RPM	Carbide SFM	Carbide RPM	Feed (in/rev)	HSS IPM	Carbide IPM
Aluminum (6061)	250	990	600	2,370	0.0128	12.7	30.3
Brass / free-machining	150	590	400	1,580	0.0099	5.84	15.6
Low-carbon steel (1018)	90	350	300	1,180	0.0124	4.34	14.6
Alloy steel (4140, annealed)	70	280	250	990	0.0129	3.61	12.8
Stainless 304	40	160	150	590	0.0104	1.66	6.14
Gray cast iron	80	320	250	990	0.0109	3.49	10.8
Titanium 6Al-4V	25	100	100	390	0.0059	0.59	2.30
Plastics (acetal)	300	1,180	500	1,970	0.0079	9.32	15.6

Metric: Vc (m/min) = SFM × 0.3048; feed (mm/rev) = in/rev × 25.4. In steel, 350 RPM × 0.315 mm/rev = 110 mm/min.

Worked example: 31/32" drill in 1018 steel

HSS drill in low-carbon steel: 90 SFM.
RPM = 3.82 × 90 ÷ 0.9688 ≈ 350 RPM.
Feed for a 0.969 in drill in mild steel ≈ 0.0124 in/rev.
IPM = 350 × 0.0124 = 4.34 IPM.

Peck cycle by hole depth

31/32" drill: depth and canned cycle
Depth	Cycle	Peck	Note
3×D = 2.906 in (73.8 mm)	G81 (no peck)	None	Up to 3×D a sharp drill clears chips on its own.
5×D = 4.844 in (123 mm)	G73 chip-break	1 × D	Chip-break pecks; full retract if chips pack (soft aluminum, stainless).
8×D = 7.750 in (196.8 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 31/32" drill

1-12 — form (roll) tap, 65% thread · tap speeds and feeds
1-20 — cut tap, 50% thread

Nearest drills

24.5 mm: 0.9646 in / 24.500 mm (-0.0042 in)
24.75 mm: 0.9744 in / 24.750 mm (+0.0057 in)
24.25 mm: 0.9547 in / 24.250 mm (-0.0140 in)
25.0 mm: 0.9842 in / 25.000 mm (+0.0155 in)

Drill speed calculator, prefilled for 31/32"Drill finder: sizes near 31/32"Fractional drill chart Decimal equivalent chart

Common questions

What is a 31/32" drill in decimal and mm?: 0.9688 in, or 24.606 mm; nearest number / letter drill: Letter Z (0.4130 in, -0.5557 in); nearest metric drill: 24.5 mm (0.9646 in, -0.0042 in).
What RPM for a 31/32" drill in steel?: In low-carbon steel (1018) an HSS 31/32" drill (0.9688 in) runs about 350 RPM at 90 SFM; a carbide drill about 1,180 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
What feed for a 31/32" drill?: About 0.0124 in/rev in mild steel, 0.0128 in/rev in aluminum and 0.0104 in/rev in 304 stainless. At 350 RPM that is 4.34 IPM in steel (IPM = RPM × IPR).
What RPM for a 31/32" drill in aluminum?: 990 RPM with HSS (250 SFM) or up to 2,370 RPM with carbide (600 SFM), feeding about 0.0128 in/rev.
What tap uses a 31/32" drill?: 1-12 (form (roll) tap, 65% thread); 1-20 (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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