ISO metric · fine

M45 × 4 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

41.5 mm

1.6339" · 67% thread

Form tap

43 mm

1.6929" · 74% thread

Open M45 × 4 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: 4 mm
Pitch Ø (basic): 42.402 mm (1.6694")
Minor Ø (internal, basic): 40.670 mm (1.6012")
Thread depth (internal): 2.165 mm (0.0852")

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 × 4
Drill	Ø in	Ø mm	Thread
1-39/64	1.6094	40.88	79%
41 mm	1.6142	41.00	77%
1-5/8	1.6250	41.28	72%
41.5 mmsuggested	1.6339	41.50	67%
1-41/64	1.6406	41.67	64%
42 mm	1.6535	42.00	58%
1-21/32	1.6563	42.07	56%

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 × 4
Drill	Ø in	Ø mm	Thread
1-11/16	1.6875	42.86	79%
43 mm	1.6929	43.00	74%
1-45/64	1.7031	43.26	64%
43.5 mm	1.7126	43.50	55%

3-wire measurement

Best wire size: 2.309 mm (0.0909")
Over wires, at basic pitch Ø: 45.866 mm (1.8057")

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