plug tap drill size

I'm sure it's out there somewhere on www but I can't find it - what is
the tapping drill size for a standard 18mm sparking plug thread?
TIA
NHH

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Try this Nick

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greetings to everyone Mike.H.

Thanks. No I don't have anything 'neerenuf' then!
NHH
Mike.H. wrote:

An old tip to get the tapping size for metric thread is the size of the thread minus the pitch. It's not 100% accurate but is very close.
John

18-1.5=16.5mm - which ISTR (link's gone T.U.) is what the chart referred to above says! Good tip.
NHH

Thanks for re-sending link Mike - actual figure in the chart is 16.8mm so 16.5mm would probably be ok if you took it easy.
NHH