This SAE Recommended Practice provides standardized dimensions for nozzle spouts and a system for differentiating between "unleaded fuel" nozzle spouts and all other fuel nozzle spouts. If emission control equipment requires unlead fuel exclusively and others fuels not meeting this specification are available, differention is accomplished by providing differences between the outside diameter of the nozzle spouts used to dispense "unleaded" and those used for all other fuels. These differences establish a basis on which fuel filler inlets that will accept only "unleaded gasoline" can be designed.