On Thu, 03 Sep 2009 00:04:33 +0100, John Rumm
wrote:

16mm is yup - remember the core size of the drill is smaller than the
flute diameter.

I never realised that. They look so rigid. This may explain why I
completely bodged up drilling through a concrete wall the other day.
I've started a new thread "drilling through concrete walls". I hope
you and Recylist can help me there. Thanks again.