The step on the die is the amount that sticks out of the clampy thingie..i use a flat file to trim up the end of the tube. Quite often the cutter leaves a tiny burr, you have to get rid of it.
I think in the first year of owning my first flare kit i broke the pin off the 3/16 die 3 or 4 times. Partly because i didnt use a vise.