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Well he isn’t asking much for them, not like he knows what he has. They are going for a lot more than $4 on eBay.

So I was at the flea market where I bought the pouch and I swear it's the same guy has this on his table. $2, I think I have $4 in the now complete set.
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I got an answer, it is a reusable heat pad cover. These were made and used from WWII to the 1990's. The bag had several changes over these years. This one is an early one, possibly WWII as it has...

Flea market pickup. Rubberized on the inside. Saw a similar one marked ORTHOPEDICS under the medical logo and called Vietnam era.

https://www.milsurps.com/images/imported/2023/04/5BFB9uk-1.jpg
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