I've seen other Elegoo Centauri Carbon exhaust ducts, but they all seem to be 4in. I wanted 3in as the amount of flow out of the exhaust fan it minimal and 4in seemed like overkill.

Note that I tweaked the lower screw tab location after these pics where taken so that it misses the that one screw a little more.
This was modeled in Onshape, so the model is available to anyone to copy and tweak as they see fit:
https://cad.onshape.com/documents/d39a802b962369dad1768e7e/w/326b3d9f16586cf9445909b0/e/28f78b4dba18b55b975fcb05?renderMode=0&uiState=697a19df666f97d671a14beb