What Size Drill Bit

M24 x 2 tap drill size

22 mm

Inches
0.8661
Inch bit
7/8"
Thread
77%

Drill a 22 mm hole before cutting an M24 thread with 2 mm pitch. The rule for metric taps is diameter minus pitch.

22 mm 24 mm thread

No metric bits? A 7/8" bit (0.8750 in) gives about 68% thread.

M24 x 2 thread and hole sizes

ThreadM24, 2 mm pitch, fine
Major diameter24 mm 0.9449 in
Tap drill22 mm 0.8661 in
Closest inch bit7/8" 0.8750 in
Clearance hole, close fit25 mm
Clearance hole, medium fit26 mm

Why 22 mm

Subtract the pitch from the diameter: 24 minus 2 is 22 mm. That leaves 77% thread, the usual target for a cut tap.

More thread than that adds almost no strength and makes the tap much easier to break. In hard or tough material, go 0.1 mm larger.

Tools for this job

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