Hi,
I use Destiny Tools 1/8th tools and they are cylindrical with 14mm (9/16ths) flute length. Given that they are cylindrical then
I'll let them hang out of the tool holder a little more and cut to 25mm depth. Its not ideal but it works certainly in soft materials,
boring in that far in steel would most likely fail.

Reduced shank would be nice, but a 1/8th shank is flexy enough without reducing it further!

Craig