headscratcher

What's the metal disk and foam thing that's on the underside of a Tecumseh gas cap designed to do?

Discovered on my first gas refill that the parts on mine fell into the gas tank. Fished them out but don't see how they stay on the shaft -- perhaps a clip broke off I haven't retreived.

Will replace cap, but for now was just wondering what that stuff does......
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Same thing happened to my old Craftsman mower. The salesman at Sears said that the disk is just a "splash guard" which prevents gas from leaking out of a filled tank. The new caps have been redesigned without the disk.

The disk was held in place by squishing down on the center plastic prong of the cap with a hot "soldering iron" type tool(not to be done anywhere near a filled gas tank!). :-)

Headscratcher