What is a 13/16" drill in decimal and mm?

0.8125 in, or 20.638 mm; nearest number / letter drill: Letter Z (0.4130 in, -0.3995 in); nearest metric drill: 20.75 mm (0.8169 in, +0.0044 in).

What RPM for a 13/16" drill in steel?

In low-carbon steel (1018) an HSS 13/16" drill (0.8125 in) runs about 420 RPM at 90 SFM; a carbide drill about 1,410 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.

What feed for a 13/16" drill?

About 0.0118 in/rev in mild steel, 0.0115 in/rev in aluminum and 0.0098 in/rev in 304 stainless. At 420 RPM that is 4.96 IPM in steel (IPM = RPM × IPR).

What RPM for a 13/16" drill in aluminum?

1,180 RPM with HSS (250 SFM) or up to 2,820 RPM with carbide (600 SFM), feeding about 0.0115 in/rev.

13/16" drill size

A 13/16" fractional drill is 0.8125 in (20.638 mm). It is the cut tap, 75% thread drill for 7/8-14.

Decimal inch: 0.8125
Millimeters: 20.638
Nearest 1/64: 13/16" (+0.0000)
Type: fractional drill

Nearest equivalents in other systems

Drills closest to 13/16"
System	Drill	Inch	mm	Difference
Number / letter	Letter Z	0.4130	10.490	-0.3995 in
Metric	20.75 mm	0.8169	20.750	+0.0044 in

Speeds and feeds: in mild steel an HSS drill starts at about 420 RPM and 0.0118 in/rev (4.96 IPM); in 6061 aluminum about 1,180 RPM.

13/16" drill speeds and feeds by material

Jobber-length twist drill, D = 0.8125 in. RPM = 3.82 × SFM ÷ D, rounded to 10. Feed per rev scales with diameter and material; IPM = RPM × IPR.

13/16" drilling speeds
Material	HSS SFM	HSS RPM	Carbide SFM	Carbide RPM	Feed (in/rev)	HSS IPM	Carbide IPM
Aluminum (6061)	250	1,180	600	2,820	0.0115	13.6	32.4
Brass / free-machining	150	710	400	1,880	0.0093	6.60	17.5
Low-carbon steel (1018)	90	420	300	1,410	0.0118	4.96	16.6
Alloy steel (4140, annealed)	70	330	250	1,180	0.0123	4.06	14.5
Stainless 304	40	190	150	710	0.0098	1.86	6.96
Gray cast iron	80	380	250	1,180	0.0103	3.91	12.2
Titanium 6Al-4V	25	120	100	470	0.0056	0.67	2.63
Plastics (acetal)	300	1,410	500	2,350	0.0073	10.3	17.2

Metric: Vc (m/min) = SFM × 0.3048; feed (mm/rev) = in/rev × 25.4. In steel, 420 RPM × 0.300 mm/rev = 126 mm/min.

Worked example: 13/16" drill in 1018 steel

HSS drill in low-carbon steel: 90 SFM.
RPM = 3.82 × 90 ÷ 0.8125 ≈ 420 RPM.
Feed for a 0.813 in drill in mild steel ≈ 0.0118 in/rev.
IPM = 420 × 0.0118 = 4.96 IPM.

Peck cycle by hole depth

13/16" drill: depth and canned cycle
Depth	Cycle	Peck	Note
3×D = 2.438 in (61.9 mm)	G81 (no peck)	None	Up to 3×D a sharp drill clears chips on its own.
5×D = 4.063 in (103.2 mm)	G73 chip-break	1 × D	Chip-break pecks; full retract if chips pack (soft aluminum, stainless).
8×D = 6.500 in (165.1 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 13/16" drill

7/8-14 — cut tap, 75% thread · tap speeds and feeds

Nearest drills

20.75 mm: 0.8169 in / 20.750 mm (+0.0044 in)
20.5 mm: 0.8071 in / 20.500 mm (-0.0054 in)
21.0 mm: 0.8268 in / 21.000 mm (+0.0143 in)
20.25 mm: 0.7972 in / 20.250 mm (-0.0153 in)

Drill speed calculator, prefilled for 13/16"Drill finder: sizes near 13/16"Fractional drill chart Decimal equivalent chart

Common questions

What is a 13/16" drill in decimal and mm?: 0.8125 in, or 20.638 mm; nearest number / letter drill: Letter Z (0.4130 in, -0.3995 in); nearest metric drill: 20.75 mm (0.8169 in, +0.0044 in).
What RPM for a 13/16" drill in steel?: In low-carbon steel (1018) an HSS 13/16" drill (0.8125 in) runs about 420 RPM at 90 SFM; a carbide drill about 1,410 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
What feed for a 13/16" drill?: About 0.0118 in/rev in mild steel, 0.0115 in/rev in aluminum and 0.0098 in/rev in 304 stainless. At 420 RPM that is 4.96 IPM in steel (IPM = RPM × IPR).
What RPM for a 13/16" drill in aluminum?: 1,180 RPM with HSS (250 SFM) or up to 2,820 RPM with carbide (600 SFM), feeding about 0.0115 in/rev.
What tap uses a 13/16" drill?: 7/8-14 (cut tap, 75% 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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