This is a remix of moononournation's awesome moon model, but with a base added that's sized for my son's ceiling fan. Not sure whether it's a standard size or not, but the size of the collar I made is 3.75 inches (outside diameter).
Searching on Home Depot's website (where I bought the fan several years ago) it looks like it's this particular fan:
Middleton 42 in. LED Indoor Brushed Nickel Ceiling Fan with Light Kit
The reason the moon itself is a somewhat odd size was due to wanting to include a brim and Cura not being smart enough to realize that the bottom of the model is not the widest point. Thus I had to make the diameter a little bit less than the 300mm size of my bed.
I hope you enjoy!
I used Fusion 360 to make the collar and Meshmixer to cut the bottom of the moon and combine the two bodies. The resultant STL file is over a gig and larger than Thingiverse allows so I've included the final Meshmixer file in a zip file instead as it's much smaller. All you need to do is save it as an STL and then slice it up. This whole process is rather resource intensive and while I'm using an inexpensive laptop, I imagine on most machines it will still take a while. Just be patient. I could only get Cura to slice it down to a resolution of 0.15mm. Trying it at 0.1mm multiple times always ended in Cura crashing.
I also included the STL for the collar simply because Thingiverse requires a file type other than Meshmixer alone.