 We, in our shop, have a tool that will flare a cut metal line, and then it will grab a hold of the plastic and hold the outside of it so it doesn't crumble and smash because you can bend that line with your fingers. How do you think you're going to shove it on with 400 pounds of pressure? So it holds the outside of it stiff while it pushes it over, but it leaves just enough room for it to expand over it.