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Thanks Scott,
I need them to be Pyrex as they are for making CDK astrographs.
Pyrex is no longer made, so I'm collecting old blanks.
Recently I acquired an old school 10" blank from a fellow ASV member, and I'm in the process of slicing it into two discs - one 25mm thick and one 15mm thick. I will be able to cut two secondary discs from the thinner one.
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