What is a 16.5 mm drill in decimal and mm?

0.6496 in, or 16.500 mm; nearest fractional drill: 21/32" (0.6563 in, +0.0066 in); nearest number / letter drill: Letter Z (0.4130 in, -0.2366 in).

What RPM for a 16.5 mm drill in steel?

In low-carbon steel (1018) an HSS 16.5 mm drill (0.6496 in) runs about 530 RPM at 90 SFM; a carbide drill about 1,760 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.

What feed for a 16.5 mm drill?

About 0.0111 in/rev in mild steel, 0.0106 in/rev in aluminum and 0.0091 in/rev in 304 stainless. At 530 RPM that is 5.88 IPM in steel (IPM = RPM × IPR).

What RPM for a 16.5 mm drill in aluminum?

1,470 RPM with HSS (250 SFM) or up to 3,530 RPM with carbide (600 SFM), feeding about 0.0106 in/rev.

What tap uses a 16.5 mm drill?

M18x1.5 (cut tap, 75% thread); M18x2.5 (cut tap, 50% thread).

16.5 mm drill size

A 16.5 mm metric drill is 0.6496 in (16.500 mm). It is the cut tap, 75% thread drill for M18x1.5.

Decimal inch: 0.6496
Millimeters: 16.500
Nearest 1/64: 21/32" (-0.0066)
Type: metric drill

Nearest equivalents in other systems

Drills closest to 16.5 mm
System	Drill	Inch	mm	Difference
Fractional	21/32"	0.6563	16.669	+0.0066 in
Number / letter	Letter Z	0.4130	10.490	-0.2366 in

Speeds and feeds: in mild steel an HSS drill starts at about 530 RPM and 0.0111 in/rev (5.88 IPM); in 6061 aluminum about 1,470 RPM.

16.5 mm drill speeds and feeds by material

Jobber-length twist drill, D = 0.6496 in. RPM = 3.82 × SFM ÷ D, rounded to 10. Feed per rev scales with diameter and material; IPM = RPM × IPR.

16.5 mm drilling speeds
Material	HSS SFM	HSS RPM	Carbide SFM	Carbide RPM	Feed (in/rev)	HSS IPM	Carbide IPM
Aluminum (6061)	250	1,470	600	3,530	0.0106	15.6	37.4
Brass / free-machining	150	880	400	2,350	0.0087	7.66	20.4
Low-carbon steel (1018)	90	530	300	1,760	0.0111	5.88	19.5
Alloy steel (4140, annealed)	70	410	250	1,470	0.0118	4.84	17.4
Stainless 304	40	240	150	880	0.0091	2.18	8.01
Gray cast iron	80	470	250	1,470	0.0094	4.42	13.8
Titanium 6Al-4V	25	150	100	590	0.0053	0.80	3.13
Plastics (acetal)	300	1,760	500	2,940	0.0066	11.6	19.4

Metric: Vc (m/min) = SFM × 0.3048; feed (mm/rev) = in/rev × 25.4. In steel, 530 RPM × 0.282 mm/rev = 149 mm/min.

Worked example: 16.5 mm drill in 1018 steel

HSS drill in low-carbon steel: 90 SFM.
RPM = 3.82 × 90 ÷ 0.6496 ≈ 530 RPM.
Feed for a 0.650 in drill in mild steel ≈ 0.0111 in/rev.
IPM = 530 × 0.0111 = 5.88 IPM.

Peck cycle by hole depth

16.5 mm drill: depth and canned cycle
Depth	Cycle	Peck	Note
3×D = 1.949 in (49.5 mm)	G81 (no peck)	None	Up to 3×D a sharp drill clears chips on its own.
5×D = 3.248 in (82.5 mm)	G73 chip-break	1 × D	Chip-break pecks; full retract if chips pack (soft aluminum, stainless).
8×D = 5.197 in (132 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 16.5 mm drill

M18x1.5 — cut tap, 75% thread
M18x2.5 — cut tap, 50% thread · tap speeds and feeds

Nearest drills

21/32": 0.6563 in / 16.669 mm (+0.0066 in)
41/64": 0.6406 in / 16.272 mm (-0.0090 in)
16.75 mm: 0.6594 in / 16.750 mm (+0.0098 in)
16.25 mm: 0.6398 in / 16.250 mm (-0.0098 in)

Drill speed calculator, prefilled for 16.5 mm Drill finder: sizes near 16.5 mm Metric drill chart Decimal equivalent chart

Common questions

What is a 16.5 mm drill in decimal and mm?: 0.6496 in, or 16.500 mm; nearest fractional drill: 21/32" (0.6563 in, +0.0066 in); nearest number / letter drill: Letter Z (0.4130 in, -0.2366 in).
What RPM for a 16.5 mm drill in steel?: In low-carbon steel (1018) an HSS 16.5 mm drill (0.6496 in) runs about 530 RPM at 90 SFM; a carbide drill about 1,760 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
What feed for a 16.5 mm drill?: About 0.0111 in/rev in mild steel, 0.0106 in/rev in aluminum and 0.0091 in/rev in 304 stainless. At 530 RPM that is 5.88 IPM in steel (IPM = RPM × IPR).
What RPM for a 16.5 mm drill in aluminum?: 1,470 RPM with HSS (250 SFM) or up to 3,530 RPM with carbide (600 SFM), feeding about 0.0106 in/rev.
What tap uses a 16.5 mm drill?: M18x1.5 (cut tap, 75% thread); M18x2.5 (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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