What is a 33/64" drill in decimal and mm?

0.5156 in, or 13.097 mm; nearest number / letter drill: Letter Z (0.4130 in, -0.1026 in); nearest metric drill: 13.1 mm (0.5158 in, +0.0001 in).

What RPM for a 33/64" drill in steel?

In low-carbon steel (1018) an HSS 33/64" drill (0.5156 in) runs about 670 RPM at 90 SFM; a carbide drill about 2,220 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.

What feed for a 33/64" drill?

About 0.0106 in/rev in mild steel, 0.0101 in/rev in aluminum and 0.0086 in/rev in 304 stainless. At 670 RPM that is 7.10 IPM in steel (IPM = RPM × IPR).

What RPM for a 33/64" drill in aluminum?

1,850 RPM with HSS (250 SFM) or up to 4,440 RPM with carbide (600 SFM), feeding about 0.0101 in/rev.

What tap uses a 33/64" drill?

9/16-18 (cut tap, 75% thread); 9/16-24 (cut tap, 75% thread); 9/16-12 (cut tap, 50% thread); 1/2-13 (Helicoil / STI insert (1/2-13×1D)).

33/64" drill size

A 33/64" fractional drill is 0.5156 in (13.097 mm). It is the cut tap, 75% thread drill for 9/16-18.

Decimal inch: 0.5156
Millimeters: 13.097
Nearest 1/64: 33/64" (+0.0000)
Type: fractional drill

Nearest equivalents in other systems

Drills closest to 33/64"
System	Drill	Inch	mm	Difference
Number / letter	Letter Z	0.4130	10.490	-0.1026 in
Metric	13.1 mm	0.5158	13.100	+0.0001 in

Speeds and feeds: in mild steel an HSS drill starts at about 670 RPM and 0.0106 in/rev (7.10 IPM); in 6061 aluminum about 1,850 RPM.

33/64" drill speeds and feeds by material

Jobber-length twist drill, D = 0.5156 in. RPM = 3.82 × SFM ÷ D, rounded to 10. Feed per rev scales with diameter and material; IPM = RPM × IPR.

33/64" drilling speeds
Material	HSS SFM	HSS RPM	Carbide SFM	Carbide RPM	Feed (in/rev)	HSS IPM	Carbide IPM
Aluminum (6061)	250	1,850	600	4,440	0.0101	18.7	44.8
Brass / free-machining	150	1,110	400	2,960	0.0083	9.21	24.6
Low-carbon steel (1018)	90	670	300	2,220	0.0106	7.10	23.5
Alloy steel (4140, annealed)	70	520	250	1,850	0.0115	5.98	21.3
Stainless 304	40	300	150	1,110	0.0086	2.58	9.55
Gray cast iron	80	590	250	1,850	0.0086	5.07	15.9
Titanium 6Al-4V	25	190	100	740	0.0050	0.95	3.70
Plastics (acetal)	300	2,220	500	3,700	0.0061	13.5	22.6

Metric: Vc (m/min) = SFM × 0.3048; feed (mm/rev) = in/rev × 25.4. In steel, 670 RPM × 0.269 mm/rev = 180 mm/min.

Worked example: 33/64" drill in 1018 steel

HSS drill in low-carbon steel: 90 SFM.
RPM = 3.82 × 90 ÷ 0.5156 ≈ 670 RPM.
Feed for a 0.516 in drill in mild steel ≈ 0.0106 in/rev.
IPM = 670 × 0.0106 = 7.10 IPM.

Peck cycle by hole depth

33/64" drill: depth and canned cycle
Depth	Cycle	Peck	Note
3×D = 1.547 in (39.3 mm)	G81 (no peck)	None	Up to 3×D a sharp drill clears chips on its own.
5×D = 2.578 in (65.5 mm)	G73 chip-break	1 × D	Chip-break pecks; full retract if chips pack (soft aluminum, stainless).
8×D = 4.125 in (104.8 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 33/64" drill

9/16-18 — cut tap, 75% thread · tap speeds and feeds
9/16-24 — cut tap, 75% thread
9/16-12 — cut tap, 50% thread · tap speeds and feeds
1/2-13 — Helicoil / STI insert (1/2-13×1D) · tap speeds and feeds

Nearest drills

13.1 mm: 0.5158 in / 13.100 mm (+0.0001 in)
13.0 mm: 0.5118 in / 13.000 mm (-0.0038 in)
13.2 mm: 0.5197 in / 13.200 mm (+0.0041 in)
12.9 mm: 0.5079 in / 12.900 mm (-0.0077 in)

Drill speed calculator, prefilled for 33/64"Drill finder: sizes near 33/64"Fractional drill chart Decimal equivalent chart

Common questions

What is a 33/64" drill in decimal and mm?: 0.5156 in, or 13.097 mm; nearest number / letter drill: Letter Z (0.4130 in, -0.1026 in); nearest metric drill: 13.1 mm (0.5158 in, +0.0001 in).
What RPM for a 33/64" drill in steel?: In low-carbon steel (1018) an HSS 33/64" drill (0.5156 in) runs about 670 RPM at 90 SFM; a carbide drill about 2,220 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
What feed for a 33/64" drill?: About 0.0106 in/rev in mild steel, 0.0101 in/rev in aluminum and 0.0086 in/rev in 304 stainless. At 670 RPM that is 7.10 IPM in steel (IPM = RPM × IPR).
What RPM for a 33/64" drill in aluminum?: 1,850 RPM with HSS (250 SFM) or up to 4,440 RPM with carbide (600 SFM), feeding about 0.0101 in/rev.
What tap uses a 33/64" drill?: 9/16-18 (cut tap, 75% thread); 9/16-24 (cut tap, 75% thread); 9/16-12 (cut tap, 50% thread); 1/2-13 (Helicoil / STI insert (1/2-13×1D)).

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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