A hotend fan, also known as a cooling fan, is a small fan usually 30mm wide and 10mm thick, that is used to cool the hotend of a 3D printer. The hotend is the part of the printer that melts the filament and extrudes it onto the build platform, and it can get very hot during the printing process. The hotend fan helps to dissipate this heat and prevent overheating, which can cause issues such as heat creep and jamming. Most 3D printer hotend fans operate at 12 or 24 volts and some are controlled by the printer's control board, running during the printing process to keep the hotend at the optimal temperature and turning off after the print is completed.