you can rent a double flaring tool from autozone and it will make a regular double flare, you can then buy an adapter for abt 5 bucks from autozone that takes in a double flare and becomes a bubble flare.

you can even just buy a euro/later GM/metric line section with nut installed from autozone (about 5 or 6 dollars for a 5 ft) and cut the line then join them with a proper brake line union fitting - all sold at autozone too.

the double union and new metric/euro/later GM line will be easiest as you get a bubble flare perfectly formed with preinstalled nut for you, and you can rent the tool to make the double flares for the union you are going to use.

lowest cost solution and no playing dodgeball with a half double to act as a DIN bubble, the base angle is incorrect for a DIN bubble flare that way and you will run a risk of blowout when you ram the brakes.

p.s. the brake line nuts are sold at parts shops too - all sorts and sizes - you need the one you see on amazon - I paid about 5 bucks for a blister pack of 4.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)