It may well fit a 203mm f7.7 Ektar, I have two similar sized Rodenstock filters (a yellow and 1.5X Tele) that fit my Ektar. Most likely sold originally for a pre-WWII Skopar or Heliar on a 9x12 (cm) Voigtlander Avus or similar.

Pre WWII filters and lens hoods were mainly push on not all lenses had a filter thread.

Ian