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BreakingChips

ISO metric · fine

M18 × 1.5 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

16.5 mm

0.6496" · 77% thread

Or 21/32 (0.6563") for 68%

Form tap

17.5 mm

0.6890" · 49% thread

Open M18 × 1.5 in the calculator

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

Thread dimensions

Major Ø
18.000 mm (0.7087")
Pitch
1.5 mm
Pitch Ø (basic)
17.026 mm (0.6703")
Minor Ø (internal, basic)
16.376 mm (0.6447")
Thread depth (internal)
0.812 mm (0.0320")

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 M18 × 1.5
DrillØ inØ mmThread
16.5 mm0.649616.5077%
21/32suggested0.656316.6768%
17 mm0.669317.0051%

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 M18 × 1.5
DrillØ inØ mmThread
11/160.687517.4653%

3-wire measurement

Best wire size
0.866 mm (0.0341")
Over wires, at basic pitch Ø
18.325 mm (0.7214")

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

Sources