This is an adapter to connect a 120mm PC fan to a 4 inch duct/pipe/dryer hose. I know there are already models like this out there, but I always find something I wish was done a little differently, so here's mine. It has the following features:

1. Fully parametric F3D file included in case you have a different sized fan, duct, or if you think I got something wrong (with labels and comments to make it easy to follow)
2. Everything slightly chamfered on the bottom for built in elephants foot compensation (not that it would affect much anyhow)
3. Chamfered top to make it easier to seat a duct to the adapter in the case you have a tight fit
4. Fairly thick attachment point for strength
5. Fairly tall attachment point to give you plenty of room for tape or whatever
6. Relatively tight fit compared to at least one of the others that I tried (but not overly tight)
7. Countersunk screw holes to hopefully reduce your chance of cracking the plastic if you're using screws with tapered heads like the standard PC fan screws

I printed this with a 0.6 nozzle at a 0.4 layer height using orange prusament PETG at 260 degrees with no fan for optimal layer adhesion. Had some wisps and stuff but overall the print quality was decent.

• Added STL for 92mm fan to 1.5" plumbing pipe (May 9, 2023)