A=440 Hz, 4 3/4 inches long x 5/8 inches wide. Suitable for home or travel, musicians or teachers, and even science enthusiasts. Nickel plated tuning fork* Suitable for violin, mandolin, and guitar. Place it on the table, place it on top of the instrument, and adjust your A string to 440 hertz* For every small but skilled player, it is necessary to adjust the sound quality every time * frequency: A-440 material: steel wire