The Grover Ukulele Humidifier has a unique design that allows you to keep it in place and refill without removing the sound hole cover. An easy and reliable way to keep your instrument protected from low humidity. Unique sound hole cover design allows you to partially or completely cover the sound hole depending on humidity levels Comes complete with moisture indicator to keep the instrument between 40-50 percent humidity E-Z fill design. You can add water without removing the sound hole cover In moderate conditions you can hang the humidifier tube between the strings without the cover The bottom of the sound hole cover has rounded edges to protect the instrument from scratching Genuine Grover Ukulele Soundhole Humidifier Manufacturers Part Number: GP720 It is important to keep your valuable instrument at the proper humidity level. Most experts agree that this is between 40% – 50% humidity. Too low and your instrument finish can be damaged and the wood can crack. Too high and your instrument will swell fret ends become sharp and it will not sound right. The GROVER® Ukulele Humidifier is the perfect product to combat these problems and to protect your expensive instrument. Our unique cover allows you to partially® or completely cover the sound hole for extreme conditions and allows you to add water without removing the cover. For very moderate conditions you can do without the cover and hang the humidifying tube between the strings. Made of soft latex the GROVER® Ukulele Humidifier is harmless to all instrument finishes.