40mm Fan Filter
I designed this filter for my 40mm fan, which I use with my Raspberry Pi. It works in conjunction with the case model "Hazi's Raspberry Pi 4 Case Lid + Ez Fan Mount / PoE-Hat Support" (https://www.printables.com/model/16102-hazis-raspberry-pi-4-case-lid-ez-fan-mount-poe-hat). However, it can certainly be used for any application involving a 40mm fan.
To use this model, you'll need to print the parts and have your preferred 3D printing glue, along with a piece of nylon stockings.

I like to apply the glue to the female part because I find it easier this way.

Next, stretch the nylon stocking over the female part until you achieve the desired tension.

After that, with some force, press the two pieces together to get a perfect fit. Use clamps to hold the parts in place until the glue sets.
I was able to achieve a very good fit using my Prusa MK4 printer. However, when I tried the same on my Ender, the fit wasn't as good. So, make sure to check your printer's tolerance to ensure proper fitting. Nevertheless, I included the STEP files for those who want to make adjustments, whether to the tolerance or any other dimension.

Once glued, trim the excess nylon, and your filter is ready.

Personally, I glued the filter to my Raspberry Pi case (Hazi's Raspberry Pi 4 Case Lid + Ez Fan Mount / PoE-Hat Support - https://www.printables.com/model/16102-hazis-raspberry-pi-4-case-lid-ez-fan-mount-poe-hat), but you can aplly this filter for inumerous uses.

The author marked this model as their own original creation.