What Size Drill Bit

M6 x 1 tap drill size

5 mm

Inches
0.1969
Inch bit
#9
Thread
77%

Drill a 5 mm hole before cutting an M6 thread with 1 mm pitch. The rule for metric taps is diameter minus pitch.

5 mm 6 mm thread

No metric bits? A #9 bit (0.1960 in) gives about 79% thread.

M6 x 1 thread and hole sizes

ThreadM6, 1 mm pitch, coarse
Major diameter6 mm 0.2362 in
Tap drill5 mm 0.1969 in
Closest inch bit#9 0.1960 in
Clearance hole, close fit6.4 mm
Clearance hole, medium fit6.6 mm

Why 5 mm

Subtract the pitch from the diameter: 6 minus 1 is 5 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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