Optics?

What are these for ? I see these all over ebay in bundles. Whould they be worth getting a mixed lot?

They look like sled optics to me. Do you have a specific link?

Heres a link to some, I have also seen some that just have very generic titles. They are usually listed as wave plates, crystals but they usually dont give specifics unless they are a KTP or specific crystal.
Laser Optics, Crystal From Telecom Company Lot 9 Packs | eBay This is only an example of what I am talking about, not necessarily the auction.

I am new to this forum and hope I get more information from this forum.
Thanks