What drill for a 1-3/4-5 roll (form) tap?

About 1.6616 in; the nearest standard drill is 1-21/32. Check your tap maker's table.

1-3/4-5 tap drill size

Use a 1-9/16 drill (1.5625 in) for a 1-3/4-5 cutting tap at 75% thread.

Drills for 1-3/4-5 (UNC)
Tap type	Drill	Decimal (in)
Cutting tap, 75% thread	1-9/16	1.5625
Cutting tap, 50% thread (hard material)	1-5/8	1.6250
Roll / form tap, 65% thread	1-21/32	1.6563

Pitch: 5.08 mm (5 TPI)
Major Ø: 1.7500
Pitch Ø: 1.6201
Minor Ø: 1.5335

1-3/4-5 tapping speeds and feeds

Feed = pitch (0.2000 in per rev). Starting points for a general-purpose HSS cut tap:

Aluminum 6061 / 7075: 150 RPM · 30.0 IPM
Free-machining / mild steel: 40 RPM · 8.00 IPM
304 / 316 stainless: 20 RPM · 4.00 IPM

1-3/4-5 tap speeds and feeds: all materials, form taps and G84 code

Open the tap drill calculator Roll tap chart Helicoil chart

Common questions

What size drill for a 1-3/4-5 tap?: Use a 1-9/16 drill (1.5625 in) for a 1-3/4-5 cutting tap at 75% thread.
What drill for a 1-3/4-5 roll (form) tap?: About 1.6616 in; the nearest standard drill is 1-21/32. Check your tap maker's table.

Other UNC sizes

Drill sizes from Machinery's Handbook and ASME B1.1/B1.13M; roll tap sizes from the form-tap formula. Tap and insert makers' tables are authoritative.

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