Diesel Fuel Line Like Compression Ferrule Only Plastic? Source?

I have one of these that is leaking pretty bad and it doesn't tighten up any more. It is the fitting from the filter to the hard pipe going over to the injection pump. I have seen them used on things like old pre-1994 Ford trucks and such. Do they have a name and what is the source? In this case it is a long obsolete Onan genset engine with a Stanadyne rotary pump.

Thanks

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Diesel Fuel Line Like Compression Ferrule Only Plastic? Source?