I wanted to shoot the eclipse. I had ordered some filters but the night before realized they were woefully inadequate. so I decided to use the Lumix and its 52mm filters and then "stack" the 77mm filters for my canon on top of them. SO I fabbed up a tinkercad friction fit adapter fit it over the 52mm and then insert the 77mm stack. Worked a treat.
it should be very tight (they are all (the filters) slightly different in size.
use a knife to "skim" the internal edges if needed to get it to fit. should be a snug friction fit.
Designed in tinkercad. made a cylinder and used 2 more cylinders as "cuts" to removed what needed to be gone.