On Mon, 20 Jul 2020 at 21:08, yorkshireman@y...
 wrote:
>
> Mick’s right of course,  It’s for counterboring, when you forgot to cut the
larger diameter first.  Not that I’ve ‘ever’ done that.  Then had to make up a
plug of the correct diameter, use the original bit to mark the centre on the
plug, and use THAT as the centre of the required counterbore.
>
> If only I had a set of counterbore bits..

Thanks all for the details, it makes sense now. The pictures posted by
Nick are clearer, on the one i posted the shape of the tip was not
very clear.

Chris