Manufacturer's part #02 MFG 017. Their price: $59.00. Made of Low expansion borosilicate glass, 38mm diameter, flatness is 1/4 wave, surface quality is 60-40 scratch and dig. 10mm thick. Polished on one side, ground but not polished on the other side. Unused. Could be aluminized to make a high reflection mirror or used as a mirror in applications where only a small amount of reflection is wanted such as sun reflection or certain laser applications. Each comes in it's own plastic case.