What drill for a 2-64 roll (form) tap?

About 0.0791 in; the nearest standard drill is #47. Check your tap maker's table.

What drill for a 2-64 Helicoil?

Drill #42 (0.0935 in), then tap with the 2-64 STI tap.

2-64 tap drill size

Use a #50 drill (0.0700 in) for a 2-64 cutting tap at 75% thread.

Drills for 2-64 (UNF)
Tap type	Drill	Decimal (in)
Cutting tap, 75% thread	#50	0.0700
Cutting tap, 50% thread (hard material)	#48	0.0760
Roll / form tap, 65% thread	#47	0.0785
Helicoil / STI insert (#2-64×1D)	#42	0.0935

Pitch: 0.3969 mm (64 TPI)
Major Ø: 0.0860
Pitch Ø: 0.0759
Minor Ø: 0.0668

Open the tap drill calculator Roll tap chart Helicoil chart

Common questions

What size drill for a 2-64 tap?: Use a #50 drill (0.0700 in) for a 2-64 cutting tap at 75% thread.
What drill for a 2-64 roll (form) tap?: About 0.0791 in; the nearest standard drill is #47. Check your tap maker's table.
What drill for a 2-64 Helicoil?: Drill #42 (0.0935 in), then tap with the 2-64 STI tap.

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.