I got a couple of those tapered cut-off blades with the bevel on top in a package deal somewhere but I never tried them until recently. I got an AXA QCTP (Chinese clone) for Christmas and decided to try one. I scratched my head for a while but never found the gumption needed to make a special toolholder so I just stacked the 2 back to back with the tapers reversed and voila! The pair clamped down in a regular toolholder just fine.
I let the outside blade extend out past the extra one just far enough to make the cut and it works just fine. Crude, buts works for me. By the way, they cut great!
They allow me to part off steel confidently for the 1st time since I got my lathe. My previous attempts usually had me ducking for cover with a snapped off chunk of HSS zinging past my head sounding like a bullet ricochet from a cowboy movie.
"Accuracy is the sum total of your compensating mistakes."
"The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton