gmax
Addicted to ArboristSite
The brand was ARTU. German made and relatively hard to find. Like all bits though you have to be careful during break through by whacking some plate at the back. If you let them just come clean out the back of a bar you'll shatter the tungsten tip like glass.
I've also used the tile bits which seem to work well despite only being designed for glass and tiles
Thanks Matt, There's some on ebay