What is a 63/64" drill in decimal and mm?

0.9844 in, or 25.003 mm; nearest number / letter drill: Letter Z (0.4130 in, -0.5714 in); nearest metric drill: 25.0 mm (0.9842 in, -0.0001 in).

What RPM for a 63/64" drill in steel?

In low-carbon steel (1018) an HSS 63/64" drill (0.9844 in) runs about 350 RPM at 90 SFM; a carbide drill about 1,160 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.

What feed for a 63/64" drill?

About 0.0124 in/rev in mild steel, 0.0129 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 63/64" drill in aluminum?

970 RPM with HSS (250 SFM) or up to 2,330 RPM with carbide (600 SFM), feeding about 0.0129 in/rev.

What tap uses a 63/64" drill?

1-1/8-7 (cut tap, 75% thread); 1-20 (form (roll) tap, 65% thread).

63/64" drill size

A 63/64" fractional drill is 0.9844 in (25.003 mm). It is the cut tap, 75% thread drill for 1-1/8-7.

Decimal inch: 0.9844
Millimeters: 25.003
Nearest 1/64: 63/64" (+0.0000)
Type: fractional drill

Nearest equivalents in other systems

Drills closest to 63/64"
System	Drill	Inch	mm	Difference
Number / letter	Letter Z	0.4130	10.490	-0.5714 in
Metric	25.0 mm	0.9842	25.000	-0.0001 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 970 RPM.

63/64" drill speeds and feeds by material

Jobber-length twist drill, D = 0.9844 in. RPM = 3.82 × SFM ÷ D, rounded to 10. Feed per rev scales with diameter and material; IPM = RPM × IPR.

63/64" drilling speeds
Material	HSS SFM	HSS RPM	Carbide SFM	Carbide RPM	Feed (in/rev)	HSS IPM	Carbide IPM
Aluminum (6061)	250	970	600	2,330	0.0129	12.5	30.1
Brass / free-machining	150	580	400	1,550	0.0099	5.74	15.3
Low-carbon steel (1018)	90	350	300	1,160	0.0124	4.34	14.4
Alloy steel (4140, annealed)	70	270	250	970	0.0129	3.48	12.5
Stainless 304	40	160	150	580	0.0104	1.66	6.03
Gray cast iron	80	310	250	970	0.0109	3.38	10.6
Titanium 6Al-4V	25	100	100	390	0.0060	0.60	2.34
Plastics (acetal)	300	1,160	500	1,940	0.0079	9.16	15.3

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: 63/64" drill in 1018 steel

HSS drill in low-carbon steel: 90 SFM.
RPM = 3.82 × 90 ÷ 0.9844 ≈ 350 RPM.
Feed for a 0.984 in drill in mild steel ≈ 0.0124 in/rev.
IPM = 350 × 0.0124 = 4.34 IPM.

Peck cycle by hole depth

63/64" drill: depth and canned cycle
Depth	Cycle	Peck	Note
3×D = 2.953 in (75 mm)	G81 (no peck)	None	Up to 3×D a sharp drill clears chips on its own.
5×D = 4.922 in (125 mm)	G73 chip-break	1 × D	Chip-break pecks; full retract if chips pack (soft aluminum, stainless).
8×D = 7.875 in (200 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 63/64" drill

1-1/8-7 — cut tap, 75% thread · tap speeds and feeds
1-20 — form (roll) tap, 65% thread

Nearest drills

25.0 mm: 0.9842 in / 25.000 mm (-0.0001 in)
25.25 mm: 0.9941 in / 25.250 mm (+0.0097 in)
24.75 mm: 0.9744 in / 24.750 mm (-0.0100 in)
31/32": 0.9688 in / 24.606 mm (-0.0156 in)

Drill speed calculator, prefilled for 63/64"Drill finder: sizes near 63/64"Fractional drill chart Decimal equivalent chart

Common questions

What is a 63/64" drill in decimal and mm?: 0.9844 in, or 25.003 mm; nearest number / letter drill: Letter Z (0.4130 in, -0.5714 in); nearest metric drill: 25.0 mm (0.9842 in, -0.0001 in).
What RPM for a 63/64" drill in steel?: In low-carbon steel (1018) an HSS 63/64" drill (0.9844 in) runs about 350 RPM at 90 SFM; a carbide drill about 1,160 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
What feed for a 63/64" drill?: About 0.0124 in/rev in mild steel, 0.0129 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 63/64" drill in aluminum?: 970 RPM with HSS (250 SFM) or up to 2,330 RPM with carbide (600 SFM), feeding about 0.0129 in/rev.
What tap uses a 63/64" drill?: 1-1/8-7 (cut tap, 75% thread); 1-20 (form (roll) tap, 65% 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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