A note on tapping holes

I normally specify a tapped hole depth of 1.5 dia for a fully threaded hole in a blind tapped hole (steel male and female). The depth of threaded hole if a plug tap is not used i.e for automatic one stage tapping would be deeper.

According to BS1936 the tapping drill should be have a depth greater than the tapped depth (clearance depth) as follows:

Less than M6 0.25 x full thread depth
M6 TO M12 0.2 x full thread depth
Greater than M12 0.15 x full thread depth

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