What drill for a 1-1/4-12 roll (form) tap?

About 1.2132 in; the nearest standard drill is 1-7/32. Check your tap maker's table.

1-1/4-12 tap drill size

Use a 1-11/64 drill (1.1719 in) for a 1-1/4-12 cutting tap at 75% thread.

Drills for 1-1/4-12 (UNF)
Tap type	Drill	Decimal (in)
Cutting tap, 75% thread	1-11/64	1.1719
Cutting tap, 50% thread (hard material)	1-13/64	1.2031
Roll / form tap, 65% thread	1-7/32	1.2188

Pitch: 2.1167 mm (12 TPI)
Major Ø: 1.2500
Pitch Ø: 1.1959
Minor Ø: 1.1598

1-1/4-12 tapping speeds and feeds

Feed = pitch (0.0833 in per rev). Starting points for a general-purpose HSS cut tap:

Aluminum 6061 / 7075: 210 RPM · 17.5 IPM
Free-machining / mild steel: 60 RPM · 5.00 IPM
304 / 316 stainless: 30 RPM · 2.50 IPM

1-1/4-12 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 1-1/4-12 tap?: Use a 1-11/64 drill (1.1719 in) for a 1-1/4-12 cutting tap at 75% thread.
What drill for a 1-1/4-12 roll (form) tap?: About 1.2132 in; the nearest standard drill is 1-7/32. Check your tap maker's table.

Other UNF 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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