This small metallic mask was used in the neck of Charactron display tubes to generate alphnumeric characters. This approach shortened the number of individual "refresh" lines needed by vector graphics displays, improving performance by making the time usually required for character display available for line drawing. Item is sandwiched between two glass plates for protection.
Datagraphix Character Mask
1 5/16 (Diam); total size (incl. plates): 2 in. 15/16 x 2 x 1 /8 (HWD)