I bought this years ago (https://forever-filter.com/forever-filter-for-drinkwell-360/) and the company no longer makes them it looks like. I needed a replacement cap so I made these.
I like the straight line/gid one better but they both should technically work.
The inner dimensions are 29.1mm and I've had some prints come out just right and a few undersized that needed a thin piece of tape around them to seal.
If you needed one of these hope it helps
The author marked this model as their own original creation.