the standard size should be the right one, but with fuel line that doesn't want to stay put or on planes where a fuel line that might fail could be fatal,small size Zip ties work well to secure the fuel tubing so it doesn't slip off the barbs for safety.
this is a OS120 pumped all the lines have zip ties for security,but make sure the lines are tight fitting even before you use the ties there just a insurance policy not a substitute for the right fit.