As above, when flaring brake pipe how much pipe should I leave above the tool before using the flaring tool?

If its the clamp affair with the g clamp thing that goes on with a set of dies then you're supposed to leave the thickness of the die in length left protruding above the flush surface of the block clamp thing.
Sorry if that's a little confusing.

If you are using a pro tool in theory none in practice 0.1 to .15 mm to get a nice plump flare.

With the "cheap" tool... I use about 5-6mm.. depends on how big a flare you want

Practice on some scrap first

I use 5mm too

from memory 6 mm - I have it written down - I did a fair bit of practise to fine tune the number.

^^^ is in range of that the peeps say above, so probably my memory is correct.

With the Machine Mart one I follow the instructions and leave level with the step on the side of the die and have had no failures.

cheers gents