It's a "spy coin" that's missing the back part, used by spies back in the day to hide microfilm and microdots in.
Here's modern day versions for smuggling/hiding micro SD cards, no dimes but from nickels on up to silver dollars.
The sole destination for direct manufacturer-to-user sales of US and Foreign hollow spy coins.
spy-coins.com
Another site showing original spy coins.
www.theregaliaspecialist.com
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