ISO metric · fine

M45 × 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

42.5 mm

1.6732" · 64% thread

Or 1-43/64 (1.6719") for 65%

Form tap

43.5 mm

1.7126" · 74% thread

Or 1-23/32 (1.7188") for 66%

Open M45 × 3 in the calculator

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

Thread dimensions

Major Ø: 45.000 mm (1.7717")
Pitch: 3 mm
Pitch Ø (basic): 43.051 mm (1.6949")
Minor Ø (internal, basic): 41.752 mm (1.6438")
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 M45 × 3
Drill	Ø in	Ø mm	Thread
42 mm	1.6535	42.00	77%
1-21/32	1.6563	42.07	75%
1-43/64suggested	1.6719	42.47	65%
42.5 mm	1.6732	42.50	64%
1-11/16	1.6875	42.86	55%
43 mm	1.6929	43.00	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 M45 × 3
Drill	Ø in	Ø mm	Thread
43.5 mm	1.7126	43.50	74%
1-23/32suggested	1.7188	43.66	66%

3-wire measurement

Best wire size: 1.732 mm (0.0682")
Over wires, at basic pitch Ø: 45.650 mm (1.7972")

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