Hose sizes refer to ID. Metal tube sizes refer to OD. I forgot the "correct" metric size, but 5/16"D hose is "close enough to fit fine". "Rated for bio-diesel" = "superior quality". It has an inner liner (Viton, I recall) that is more resistant to all the extras put in fuels today. I try to use it in my gas cars too. You can use regular rubber fuel hose, but probably won't last as long.

Fill the new primary fuel filter to the brim w/ diesel, then spin it on (actually center bolt pulls it up). Per manual, crack the return banjo fitting (aft) as you operate the hand pump to purge all air up to the IP and tighten as you keep pumping. You may still get some air in, but it should eventually sweep thru. If hard to start, crack the fuel tube nut at the top of each injector (17 mm wrench, I recall), one at a time, as you crank and tighten it slowly as fuel dribbles out. That should get all the air out. That is also a good cylinder check when running. You should note each cylinder fall out (engine gets rougher) as you crack each nut, since the fuel dribbling out isn't going thru that injector (requires 1600 psig to pop open your non-turbo injectors).

BTW, good your engine is diesel. My sister once had me look at a ~1970's Volvo wagon w/ electronic fuel injection. Unlike modern engines, it used short rubber hoses off the injectors and each was dribbling gas - i.e. major fire hazard. Good your wetness is diesel since it won't ignite from a spark. When MPFI injection came out (~60 psig), I predicted future engine fires. While we do occasionally see burnt gas cars, it seems no worse than w/ carburetors, probably thanks to Viton O-rings.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans