Simple connector for 120mm PC fans and 4 inch dryer duct (not a recommended application of a 120mm PC fan but it works for my purposes, maybe it'll work for yours too). Distance from the back of the fan to the start of the 4 inch section is 40mm and the piece is 2.4mm thick in most places (some chamfering). I printed this in translucent blue PETG (Overture) with no supports.
The author marked this model as their own original creation.