Just wondering
I now know that there were 3 styles of plastic fuel lines installed int the cars
Earliest - clear/opaque
Mid - clear/opaque w/barbed steel ends at front
late - Black plastic

My question is on the "Mid" yr version : How were those steel finttings installed?
some sort of heat process?

Maybe this is Q for the Dr.

Probably the same way the metal fittings are installed on the brake line tubes from the master cylinder to the reservoir. May be heat shrunk to withstand fuel pressure and not need clamps.

I think they are heated which softens the tubing and the tube is forced inside. When it cools it shrinks. Unlike shrink tubing that is oversize and shrunk with heat.