What drill for a M3×0.5 roll (form) tap?

About 2.78 mm; the nearest standard drill is 2.80 mm. Check your tap maker's table.

What drill for a M3×0.5 Helicoil?

Drill 3.4mm (3.40 mm), then tap with the M3×0.5 STI tap.

M3×0.5 tap drill size

Use a 2.5mm drill (2.50 mm) for a M3×0.5 cutting tap at 75% thread.

Drills for M3×0.5 (Metric)
Tap type	Drill	Decimal (mm)
Cutting tap, 75% thread	2.5mm	2.50
Cutting tap, 50% thread (hard material)	2.6mm	2.60
Roll / form tap, 65% thread	2.80 mm	2.80
Helicoil / STI insert (M3×0.5×1D)	3.4mm	3.40

Pitch: 0.5 mm
Major Ø: 3.00
Pitch Ø: 2.67
Minor Ø: 2.46

Open the tap drill calculator Roll tap chart Helicoil chart

Common questions

What size drill for a M3×0.5 tap?: Use a 2.5mm drill (2.50 mm) for a M3×0.5 cutting tap at 75% thread.
What drill for a M3×0.5 roll (form) tap?: About 2.78 mm; the nearest standard drill is 2.80 mm. Check your tap maker's table.
What drill for a M3×0.5 Helicoil?: Drill 3.4mm (3.40 mm), then tap with the M3×0.5 STI tap.

Other Metric 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.