You have to love it! The military way of describing things… this item is: Filter Assembly 1 each. Has 2 part numbers shown on the package: 2900-292900 and 202-10-68. Also Cont. No: AF 33(600)32284. Mfg by J. A. Maurer Inc, NY. It's a clear filter mounted in a ring with a 36.2 mm diameter thread. Overall, the part is 4 mm thick. 30.5 mm clear aperture. Apparently, its function was purely protective, as no optical characteristic is mentioned. Made in 1957, Unused.