That isn't a "usual EFI pump." I'm referring to OE replacement & similar.

I went with 3/8" on my slant 6 car. Mostly because -5AN stuff is pretty much non-existent.

AN dash sizes are easy once you know the simple rule. The fractional size equivalent is what-ever the dash size is over 16. So a -10 is equal to a 10/16" or 5/8", a -3 is equal to a 3/16"
The rub is that the actual diameter under control is the ID, even though the size spec'd is the OD, and those are based on the fractional copper tube equivalent's ID.
​