Prusa i3 MK3 3D Printer Parts Super Silent Cooling Fan 4010 Hydraulic Bearing Fan 5V 40*40*10 Cool Fan Cooler Radiator Sleeve Specifications Rated voltage: 5V Dia. of cooling fan: 40 mm Dimensions: About 40 x 40 x 10 mm Cable length: About 750mm Advantage:supper silent Note: the fan has two sides,but the side with sticker must be always facing the hotend (not visible when the fan is mounted).Otherwise,the cooling won't work properly.