What is this jar lid?

[dogtx]

Found this some time ago.
It was still screwed to the broken jar.
What's up with the middle baby top on the top?

 

[dogtx]

More pics

 

[dogtx]

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[dogtx]

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[dogtx]

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[dogtx]

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[dogtx]

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[epackage]

...Jar section would be the spot to post this question...

 

[MichaelFla]

Lid is from a Woodbury Improved jar. Zinc lid with mini zinc lid which which was used as a vent to allow air in when breaking the seal. The mini lid alone can be worth over $100. The rest of the lid is worth roughly $25- $35. Great find! Let me know if you're interested in parting with it.

 

[dogtx]

On top of the glass lid itself is a smaller threaded piece with a little
hole through it. I looks to be that it it's self had a metal lid.
What is it?