A 40x40X15 adapter you can drop a 30mm fan into to mount it in place of a 40mm fan.
Going to use this for my Prusa extruder assembly, since i kinda broke all my 40mm fans.
The 30mm fan is held in place by the screws used to secure the 40mm adapter to wherever
Increased the diameter of the M3 holes to 4mm to make sure everything fits.
Added a cutout for the 30mm fan's wiring.
Added a 10mm variant that has no funnel, still press fits a 30mm fan.