Opening tuning heads to make the ukulele easy to maintain and stay in key with adjustable tightness Please download the professional tuner App to adjust intonation by the tuning heads Strings of nylon material is flexible, soft and smooth tactility, and not scratching hands with small friction resistance The design of bridge delivers the complete frequency effectively, and also delivers the rich timbre. By plucking the strings to vibrate the air inside, then sound masde from the hole.