Print the filter holder 2 times. Sandwich the filter between the 2 filter holders and glue them together. I used E6000 glue. Stay safe and only purchase certified filters.
Compatible with the Hadley telescope: https://www.printables.com/model/224383-astronomical-telescope-hadley-an-easy-assembly-hig
The author remixed this model.
Converted the cover to use it as a filter holder