Lincoln OEM Vented Fuel Cap 9SS20541, newer style! Fits SAE 300,400,500 with plastic/composite tanks. Also, fits Air Vantage, Classic, Commander and Rangers that have large vented caps AND composite tanks. The neck of your tank should be about 3-1/2" diameter measured to outside of threads. This cap has an overall Outside of 4-1/4" with 3-1/2" threads on inside. NOT FOR STEEL TANKS! Make sure you need THIS CAP! NO RETURNS!