"Specified dimensions: 1.520 inches in diameter, with a center thickness of 0.210 inches; requires .0003 fir, 1 minute centering accuracy; manufactured from Schott optical glass (type 517642), BK-7 grade A, stain-free, annealed finely according to MIL-G-174 standards."
AGAV
Main Item Identification Information
"The item is identified as AN/AAQ-9, an Infrared Detecting Set."