Grover GP720 Ukulele, Black 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