What drill for a 0-80 roll (form) tap?

About 0.0545 in; the nearest standard drill is #54. Check your tap maker's table.

What drill for a 0-80 Helicoil?

Drill #49 (0.0730 in), then tap with the 0-80 STI tap.

0-80 tap drill size

Use a 3/64" drill (0.0469 in) for a 0-80 cutting tap at 75% thread.

Drills for 0-80 (UNF)
Tap type	Drill	Decimal (in)
Cutting tap, 75% thread	3/64"	0.0469
Cutting tap, 50% thread (hard material)	#55	0.0520
Roll / form tap, 65% thread	#54	0.0550
Helicoil / STI insert (#0-80×1D)	#49	0.0730

Pitch: 0.3175 mm (80 TPI)
Major Ø: 0.0600
Pitch Ø: 0.0519
Minor Ø: 0.0447

Open the tap drill calculator Roll tap chart Helicoil chart

Common questions

What size drill for a 0-80 tap?: Use a 3/64" drill (0.0469 in) for a 0-80 cutting tap at 75% thread.
What drill for a 0-80 roll (form) tap?: About 0.0545 in; the nearest standard drill is #54. Check your tap maker's table.
What drill for a 0-80 Helicoil?: Drill #49 (0.0730 in), then tap with the 0-80 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.