The OH-18 Ukulele Humidifier by Oasis has two unique features, the mounting system allows the humidifier to hang horizontally inside the ukulele rather than vertical (like the guitar humidifier) and the humidity output is about 50% of the Royal Blue Oasis guitar humidifier, to accommodate the smaller instrument size. This also allows the humidifier to last twice as long between refills. An active lifespan of 24 months, replace the humidifier every two years. • MFSKU OH-18 • UPC 898775001328