Supply is 5/16" I.D. and return and vapor lines are both 1/4" I.D. Be sure to use SAE rating of 30R9 or 100R6 for all hoses. 30R6 and 30R7 are common offerings, but are inadequate for fuel injection pressures. And use band clamps instead of the 'ladder' type of worm-roller clamps, as they won't cut into the hose as much.