This is a geared moor cooling jacket for a Felfil Evo extruder motor (36mm diameter x 60mm length) and a 40x40mm 5V fan.
Noticed that when coolded Felfil Evo extruder motor working at full speed maintains a constant power draw contrary to uncooled.
So here is a cooling jacket.
Practically requires no post processing
I just made screw holes 2.5mm in diameter so I can screw in 3mm screws directly or with a nut. Used 4 M3 20 mm long screws and nuts to mount the fan and in case the jacket would appear loose (for me it printed airtight) one can use two more 3mm screws and nuts to fixate the jacket in desired position.