What is a 18.5 mm drill in decimal and mm?

0.7284 in, or 18.500 mm; nearest fractional drill: 47/64" (0.7344 in, +0.0060 in); nearest number / letter drill: Letter Z (0.4130 in, -0.3154 in).

What RPM for a 18.5 mm drill in steel?

In low-carbon steel (1018) an HSS 18.5 mm drill (0.7284 in) runs about 470 RPM at 90 SFM; a carbide drill about 1,570 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.

What feed for a 18.5 mm drill?

About 0.0114 in/rev in mild steel, 0.0109 in/rev in aluminum and 0.0094 in/rev in 304 stainless. At 470 RPM that is 5.36 IPM in steel (IPM = RPM × IPR).

What RPM for a 18.5 mm drill in aluminum?

1,310 RPM with HSS (250 SFM) or up to 3,150 RPM with carbide (600 SFM), feeding about 0.0109 in/rev.

What tap uses a 18.5 mm drill?

M20x1.5 (cut tap, 75% thread); M20×2.5 (cut tap, 50% thread).

18.5 mm drill size

A 18.5 mm metric drill is 0.7284 in (18.500 mm). It is the cut tap, 75% thread drill for M20x1.5.

Decimal inch: 0.7284
Millimeters: 18.500
Nearest 1/64: 47/64" (-0.0060)
Type: metric drill

Nearest equivalents in other systems

Drills closest to 18.5 mm
System	Drill	Inch	mm	Difference
Fractional	47/64"	0.7344	18.653	+0.0060 in
Number / letter	Letter Z	0.4130	10.490	-0.3154 in

Speeds and feeds: in mild steel an HSS drill starts at about 470 RPM and 0.0114 in/rev (5.36 IPM); in 6061 aluminum about 1,310 RPM.

18.5 mm drill speeds and feeds by material

Jobber-length twist drill, D = 0.7284 in. RPM = 3.82 × SFM ÷ D, rounded to 10. Feed per rev scales with diameter and material; IPM = RPM × IPR.

18.5 mm drilling speeds
Material	HSS SFM	HSS RPM	Carbide SFM	Carbide RPM	Feed (in/rev)	HSS IPM	Carbide IPM
Aluminum (6061)	250	1,310	600	3,150	0.0109	14.3	34.3
Brass / free-machining	150	790	400	2,100	0.0089	7.03	18.7
Low-carbon steel (1018)	90	470	300	1,570	0.0114	5.36	17.9
Alloy steel (4140, annealed)	70	370	250	1,310	0.0120	4.44	15.7
Stainless 304	40	210	150	790	0.0094	1.97	7.43
Gray cast iron	80	420	250	1,310	0.0099	4.16	13.0
Titanium 6Al-4V	25	130	100	520	0.0055	0.72	2.86
Plastics (acetal)	300	1,570	500	2,620	0.0069	10.8	18.1

Metric: Vc (m/min) = SFM × 0.3048; feed (mm/rev) = in/rev × 25.4. In steel, 470 RPM × 0.290 mm/rev = 136 mm/min.

Worked example: 18.5 mm drill in 1018 steel

HSS drill in low-carbon steel: 90 SFM.
RPM = 3.82 × 90 ÷ 0.7284 ≈ 470 RPM.
Feed for a 0.728 in drill in mild steel ≈ 0.0114 in/rev.
IPM = 470 × 0.0114 = 5.36 IPM.

Peck cycle by hole depth

18.5 mm drill: depth and canned cycle
Depth	Cycle	Peck	Note
3×D = 2.185 in (55.5 mm)	G81 (no peck)	None	Up to 3×D a sharp drill clears chips on its own.
5×D = 3.642 in (92.5 mm)	G73 chip-break	1 × D	Chip-break pecks; full retract if chips pack (soft aluminum, stainless).
8×D = 5.827 in (148 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 18.5 mm drill

M20x1.5 — cut tap, 75% thread
M20×2.5 — cut tap, 50% thread · tap speeds and feeds

Nearest drills

47/64": 0.7344 in / 18.653 mm (+0.0060 in)
23/32": 0.7188 in / 18.256 mm (-0.0096 in)
18.75 mm: 0.7382 in / 18.750 mm (+0.0098 in)
18.25 mm: 0.7185 in / 18.250 mm (-0.0098 in)

Drill speed calculator, prefilled for 18.5 mm Drill finder: sizes near 18.5 mm Metric drill chart Decimal equivalent chart

Common questions

What is a 18.5 mm drill in decimal and mm?: 0.7284 in, or 18.500 mm; nearest fractional drill: 47/64" (0.7344 in, +0.0060 in); nearest number / letter drill: Letter Z (0.4130 in, -0.3154 in).
What RPM for a 18.5 mm drill in steel?: In low-carbon steel (1018) an HSS 18.5 mm drill (0.7284 in) runs about 470 RPM at 90 SFM; a carbide drill about 1,570 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
What feed for a 18.5 mm drill?: About 0.0114 in/rev in mild steel, 0.0109 in/rev in aluminum and 0.0094 in/rev in 304 stainless. At 470 RPM that is 5.36 IPM in steel (IPM = RPM × IPR).
What RPM for a 18.5 mm drill in aluminum?: 1,310 RPM with HSS (250 SFM) or up to 3,150 RPM with carbide (600 SFM), feeding about 0.0109 in/rev.
What tap uses a 18.5 mm drill?: M20x1.5 (cut tap, 75% thread); M20×2.5 (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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