Updated: This cooling box is for TAZ3 3D printer, it uses a 50 mm muffin fan, it has three outlets: one outlet is for cooling extruded filament (good for PLA printing), one for keeping the extruder motor above it cool, and one for giving active cooling to the hot-end heat sink. The update is the addition of exhaust hole to the hot-end because I found that active cooling enables you to use more different brands of ABS filaments without which the Hobbed Bolt likes to dig into the filament too much. You can close the holes you are not using with a scotch tape anytime... You need two m3 6mm screws for mounting it on the right side of the hot end assembly, also it uses four Heat-set inserts (M2.5) for mounting the fan.