Junk Box Whatsit

[randywa]

I found this in a $2 yard sale mystery box. I thought maybe some kind of thermometer. The plastic tube doesn't have a hole in the point and seals with an o ring. I haven't been able to find any markings on it. Any ideas? Thanks for any help.

 

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[Anduril]

Maybe..
1) some sort of pressure-based, or temperature-based metering valve
2) a pen for a seismograph