Ceramic Plate / Disc, 6" Diameter x .149" Thick

Description

New old stock.
In great condition and in sealed factory bubble wrap as packaging.
No identifying markings on the part or packaging.
Made from ceramic or porcelain.
The disc used for the photos is unwrapped and dirty from  handling and is not being sold.
Came from a collection of Applied Materials spare parts so it's very likely from Applied Materials.
If this is something you recognize, please let me know. It would be much appreciated.
Approximate Dimensions:
See sketch in with the photos