So, I have a 4020 Hotend fan on my Ender 3 and wanted to add a 5015 fan duct using the petsfang blokhead models to it. Now, the original blokhead only allowed for a 4010 fan, I found this here, and just stretched the middle part of the lighter bullseye by 1cm to allow for the fit of the 4020.
Not really tested yet, so use with caution
The author remixed this model.