I have a 1985 300D that I have been running with biodiesel. I started with B20. This caused the fuel lines (as I expected) to soften and weep. I have replaced all of the fuel lines under the hood with fluoroelastomer tubing. So far for whatever reason the fuel lines at the tank are still firm, however, I want to prepare to replace them with fluoroelastomer tubing. I question is concerning the fitted fuel line that connects to the in-tank fuel filter. I am trying to find a fitting to connect to the filter, but I am having difficulty determining the thread size. Does anyone know what size of thread this is?
Thank you,

Don't know either but its a metric pipe thread................

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Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
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Section 609 MVAC Certified
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche