CST/Berger 63-2011-B Precision Prism Only in Canister Black USA
2-1/2" (62.5mm) prisms are hermetically sealed to prevent loss of range or accuracy due to contamination.
Will fit any prism holder with a 5/8" x 11 female thread.
Overall diameter approximately 2-7/8"
Aeronca x 8 Caldwell 3rd build