My all metal hotend needed more cooling - a 40mm x 10mm fan was better but not enough - so I mounted a 40mm x 20mm fan - now it is perfect.

the 40x20 fan has m4 screws and is way heavier than the 40x10 - so I made a design that brings the fan as near to the hotend as possible - and, of course, it has M4 threads.

Use PETG or ABS or anything else that can handle more heat than PLA.
I used a litte peace of aluminium foil at the bottom of the adapter - just in case.

UPDATE - added a M3 Version

SecKit SK GO 350

Doesn't Matter

No

Nozzle 0.4 / Layer 0.2

100%