Tips on making your own transmission lines

there is such a thing as a bubble flare. Its jus a bubble on the end of the line like on old carb lines where rubber fuel line is clamped on. It is hard to find a flare tool that will make a true bubble flare. You can kind of do it with the double flare tool if you are careful. (the idea is to be able to push on the rubber line without "shaving rubber" and it ending up in your lines. The nice bubble prevents this and also keeps the rubber line from coming off).
On the subject of trans lines, I remember an old mechanic friend of mine back in the eighties that used to use some kind of nylon line with compression fittings. I never questioned this as he was a long time mopar dealer mechanic back in the 70's but I wonder what kind of line it was exactly. I know it was cheap and easy. I think I would vote for the steel 5/16 line.