The small piece feeding the pump is #10 into a 100micron/10 micron out and #10 all the way to the "Y" under the hood then #6 coming out of the "Y" feeding the rails and # 6 going into the regulator. The return coming out of the regulator is #6 for 30 inches(just behind the upper control arm) then increases to #8 braided line all the way back to the tank. A-1000 pump.