ISO metric · fine

M30 × 3 tap drill size

For general work, OSG suggests 65–70% of full thread. Harder materials and deep holes want less; the calculator sets it from your material.

Cut tap

27.5 mm

1.0827" · 64% thread

Or 1-5/64 (1.0781") for 67%

Form tap

28.5 mm

1.1220" · 74% thread

Or 1-1/8 (1.1250") for 70%

Open M30 × 3 in the calculator

Pick your material for its % of thread, tapping RPM and the rigid-tap code.

Thread dimensions

Major Ø: 30.000 mm (1.1811")
Pitch: 3 mm
Pitch Ø (basic): 28.051 mm (1.1044")
Minor Ø (internal, basic): 26.752 mm (1.0532")
Thread depth (internal): 1.624 mm (0.0639")

Basic sizes of the 60° form. Tolerance classes (6H) set the limits around them.

Cut tap drills

For a cutting (fluted or spiral) tap. Every standard drill from 50% to 85% thread; suggested rows are in the 65–70% band.

Cut tap drills for M30 × 3
Drill	Ø in	Ø mm	Thread
1-1/16	1.0625	26.99	77%
27 mm	1.0630	27.00	77%
1-5/64suggested	1.0781	27.38	67%
27.5 mm	1.0827	27.50	64%
1-3/32	1.0938	27.78	57%
28 mm	1.1024	28.00	51%

Form tap drills

A form (roll) tap displaces metal instead of cutting it, so it needs a bigger hole. Every standard drill from 50% to 85% thread; suggested rows are in the 65–70% band.

Form tap drills for M30 × 3
Drill	Ø in	Ø mm	Thread
28.5 mm	1.1220	28.50	74%
1-1/8suggested	1.1250	28.58	70%
1-9/64	1.1406	28.97	50%

3-wire measurement

Best wire size: 1.732 mm (0.0682")
Over wires, at basic pitch Ø: 30.650 mm (1.2067")

For the external thread (the screw). The best wire touches the flanks at the pitch diameter.

Sources

ISO 261 / ISO 262 — ISO general purpose metric screw threads: general plan and selected sizes
OSG — Tap drill size and pitch diameter limit chart (formula, suggested % of full thread)
Cutting Tool Engineering — "Threads will roll": form tap hole size = D − 0.0068 × % / TPI
ASME B94.11M — Twist drills (fractional, number, letter and metric sizes)
NIST (NBS) Letter Circular 23 and Pratt & Whitney — three-wire thread measurement, best wire size