The Hydra by Quality Importers - Optional External Fan - Small helps air circulation in your humidor to optimize humidification. A total of 3 external fans can be used with the Hydra SM (small) humidifier; sold separately. Each fan kit comes with a fan, adapter and splitter. The splitter allows for up to three additional fans to be used. For the Hydra SM, the kit can be plugged into the Fan port to allow the external fans to cycle at the same time as the built-in fan, or you can also plug the fans into the port marked DC power which will allow the fans to operate continuously. Fits Hydra SM.