Button backs????????

[rustydigger]

I have found these three items the third one was today so I have to ask. What are they? The two rectangled ones have 4 letters on them, 1 says COSM no particular order or starting point. The 2nd one says FCUC, also no particular starting point. The rounded object I'm not sure its related or in the same category. So if anyone can help it would be nice to know.
Thanks for looking

 

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[Bigcypresshunter]

If found on the beach, they are from bathing suits or straps..

 

[Bigcypresshunter]

Most may be bathing cap strap buckles. http://www.treasurenet.com/treasures/feature/200410.htm

 

[rustydigger]

Thank you makes a lot of sense because where I found them a lot of stuff from that era is found.