> Now as to the corresponding drill size, that becomes a bit more
> difficult. You need to drill a hole the size of the bottom of the threads.
> Such information is readily available in machinist's handbooks for SAE but
> I've never seen it for metric. That certainly doesn't mean it's not
You can find practically anything you want on the web, including many metric tap drill size charts. Here's one:
(all one line of course).
email@example.com (John V. Everett)