While I was connecting the fuel line to the filter and carbs I realized that the fuel fittings on the crabs are 3/8 (9.5mm) whilst my fuel line is 5/16 (8mm). Is it ok if I use a fitting from 5/16 to 3/8? Do i have to replace the whole fuel line? (Braided and very expensive!!!)

Regards

it will fit if you push hard enough

I came across the same thing this week too.
I'm just going to get a fuel filter with different (the correct) size inlet and outlet.

Not found a cheap one yet though.