This is a VITON Gasket cut slightly oversized in it's outside diameter so it will stay centered in the cap with no retention ring guiding it. It is best to still use the flange with this gasket, but you must remove all remains of the gasket retention ring molded on it so it appears like the one pictured above. This gasket effectively seals the entire opening of the can as opposed to to the previous gasket and flange working together to seal the can. Please keep in mind that this gasket will not be retained inside the cap and will fall out when you take the cap off.
This gasket will also work without the flange if it were absolutely necessary. This gasket can also be used as an EMERGENCY SEAL with just the outer shell cap. You would just need to put a small amount of lubricant (spit works) between the gasket and the cap before tightening, so the cap can slip on the gasket during tightening.
Please email if you have any questions about whether this will work for you prior to buying.