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When I need to put flexible hose over hard line that I've cut, I usually use my double flaring tool to put a little "bubble" at the end of the tubing just to make sure the hose and clamp aren't able to slip off of the tubing. I set up the tube in the clamp like normal, put the mandrel in the tube like the first step of a double flare but I only tighten it down enough to expand the tube and make it just a bit wider than nominal.
That's what I was thinking should happen if cutting the hard line. I even dug out the flaring tool, but then decided to just loop flexible back to the new spot. Was nervous to cut the hard line and cross the path of no return.
If I cut the steel I'd probably use a compression adapter from steel to nylon fuel line to the filter. The nylon fuel line kits hold 60+ lbs of pressure on gas vehicles and I've used the kits to eliminate rusty lines.