Difficulties with filling the tank all the way up

The actual filler nozzle of the pump was larger and fit better in the old car's fill tube. When unleaded gas came out (you used to have a choice - leaded or unleaded), new cars that took unleaded only (catalytic converter) had a smaller neck in the car filler tube that would keep you from accidentally filling with leaded and killing the converter. Now old cars have big tubes and all the gas nozzles are small.